I find these predictions for speedy Japanese expansion in both these scenarios to be *massive* overestimates.
Chiron is almost treating it as if any teleportation or time-travel of a territory also comes with a message from the supernatural spirits that says, "You are now in a new location, show us how fast you can expand, go!" and the political leaders of the teleported land are *compelled* to go for maximum expansion, for our entertainment, as if they are in a boardgame.
I don't see any reason to assume or expect any of this.
Just because you don't see it, doesn't mean its not valid. That is an A Priori statement.
On the 1854 scenario:
No. 1854 Japan isn't in shape to just go imperializing right away. Japan needs to sort out its internal situation and get a real national government going first and figure out how to react to foreigners demanding access. In OTL, Japanese adventurers didn't start doing overseas expeditions until 20 years after the Perry expedition. (the Taiwan punitive expedition). While trying to copy western ships, Japanese crews weren't skilled enough to crew western style steam-ships across the ocean until the 1870s.
The Shogun, Tokugawa Iesada, is in firm control at this time. Nor do they need "western ships" to reach Hawaii. Meiji doesn't become a thing till Tokugawa Yoshinobu just implodes in 1867 and effectively resigned.
While Hawaii is weaker, smaller population neighbor than Korea, China, or China's Taiwan province, it was frequented in the 1850s and beyond by American, British, French, and Russian ships that could blow anything the Japanese had and could operate out of the water. Also, while Japan on the map is somewhat close to Midway island, that is still a long distance (like at least Key West Florida to Maine) from Midway to Oahu or Hawaii's big island.
And irrelevant, as neither of those powers cared about Hawaii till the 1890s when the US began the process of annexing it. What matters is who can pour in troops faster and sustain the attrition and will to fight longer.
American interests were getting pretty strongly established in Hawaii from the 1840s and 1850s. It's proximity to the new Japanese trading partner will probably only accelerate that US interest.
Those interests had no teeth till the late 1880s and 90s, till then, Congress wasn't going to bankroll an intervention when it had large areas of its interior to still pacify and Mexico's instability to the south. Britain is too busy elsewhere to really do anything other than maybe sting. And the Japanese have a cultural memory of going up against a superior navy and it not mattering one way or another to the ground war they fought in Korea.
The French might contest this, but they were also tied up elsewhere. Russia doesn't really care about Hawaii, too busy elsewhere. Germany wasn't a thing at this moment of time.
On the 1540 scenario:
The Japanese don't have reliable or sophisticated long-distance sailing technology at this time. Their traders, monks, and pirates, mainly traveled short distances on nearly inland seas like the the Sea of Japan, Yellow Sea, South China Sea. They can investigate, but in most directions, they will be shocked to find...nothing.
The Japanese merchants were trading as far away as Byzantium in the late 790s, multiple byzantine instruments made their way to the Heian Court in this time period. The Japanese also captured multiple ocean going vessels from the Mongols.
They had extensive ocean contacts with India, Indonesia, and with the Siberians and Inuits. They can also do star reckoning and calculate very accurately how far they have shifted and where to go to re-establish contact with China and other trade partners.
They had the technology, the scientists, knowledge, and the resources to do this. Its a matter of the Daimyo ordering the investments be made.
Unless Japanese leaders get a detailed briefing with maps and so on from the ASBs, all the Japanese can tell went down is that sunset and dawn hours are messed up, and in a couple weeks/months they'll find that trading neighbors like Korea, China, and the Ryukyu Kingdom have vanished. They won't know what happened, and can only guess at things like maybe the sea God Ryujin/Watatsumi grew angry and swallowed their neighboring countries. Their focus will be as much on propitiating angry sea gods as exploring the edges of their new surroundings.
Most Nobles will figure out quickly from their court's wise men that they shifted far away from their normal spot and exactly how far they have to adjust sea voyages. Expeditions will be sent out immediately. The propitiating will be a matter of course, but that is mainly for the gullible sheep of the masses. Most nobles are more practical.
No they didn't. They had no matchlock technology for personal firearms anything like the European muskets or arquebuses of the day. Don't confuse the fact that they had the good blacksmithing skills to soon start copying them once they had some and saw them in action with the idea that they had these pre-western contact. Personal weapons were still archery, sword, and spear-based. Cannons were probably around, maybe small crew weapons like a fire lance or hand cannons, but the shooter in those cases always needs helpers to fire and aim their weapons.
Dude, they first got a taste of gunpowder in the Mongol Invasions and captured quite a bit of it. Teppō from 1270 was known in Japan and fire lances were in widespread use by the 15th century. 1510 matchlock pistols of Chinese origin are recorded in use. Even if the Portuguese never arrived, the Japanese were well on their way to an independently developed firearms industry and was experimenting with flintlocks before the Tokugawas enforced Sakoku. This Eurocentrism is unfounded.
Also the Japanese produced more guns in the 16th Century than the rest of the world combined by a vast amount and was transitioning to an all gun army when the Shogunate went Sakoku for everyone. Europe in that same timeframe was pikes, and more pikes, and stick a few guns here and there. So tactically the Japanese were outpacing Europe, so good thing Tokugawa threw out the baby with the bath water for them.
No. Why would they run into the Spanish galleons? The Spanish galleons went way to the south, in the tropics, and they never went to Hawaii. The whole premise presented here vastly underestimates distances in the Pacific. Distances between each major segment of the Pacific where there are islands and people are vast, like distances between Europe and the US east coast, and the Japanese have no experience, and no motive, to go that far.
Because, their Astronomers can crunch numbers and star positions, Daimyos have an incentive to figure out what is out there, and they do have cultural and trade ties with the world in both obvious and subtle ways few appreciate and want to re-establish contact as well as assess the new strategic outlook. Many of them are also dependent on taxing said trade as well.
Seriously dude, ditch the Eurocentric nonsense and look at what other cultures actually had done well before Europe came along. Especially the Oceania Cultures who used canoes to expand and trade from Africa to the Americas and traded with the Aborigines of Australia and absent European Conquest, may even have settled in Australia.
For Japan which is far more capable than the Oceanian Cultures, exploring south is a strategic imperative and easier logistically for them as they have proper ocean going ships which can carry large amounts of supplies for said trips.
