Spring year 2 right? Or are people really unlocking the walnut room in spring year 1?
This is spring one and yeah is definitely quite crazy (especially getting there in the first 2-3 weeks)
Yeah Spring Y1 sounds crazy! Reveal your secrets Gorilla
Haha, it's not so much secrets as very careful and well executed playing. Clay farming for early cash (or fishing but it's slower), deep in the mines ASAP, then something like geode or void/diamond farming to buy the joja forms basically as fast as possible. You can also choose to complete both the boiler room and all vault bundles on day 6 with the cc which buys an extra day but that's incredibly tough to pull off.
The hardest thing about the whole process is really the hardwood, if you just want to get there in spring though it's not too bad, instead of that first mad rush for joja completion you can pour some cash into axe/pick upgrades, going for wood basically every day possible.
Rolling some cash into skull cavern runs is basically necessary for easy cash/iridium/batteries, which should see you with a boat completion ideally around the early fourth week (20th-23rd). Again hardwood is the tough part but you get a good chunk of the hardwood just from the farm which only necessitates about 9 visits to the secret woods.
Once you're on the island, it's very much a mad dash. I've been able to get 100 walnuts in just about 3 days, but it's possible to do it in 2. It's even harder than you think as many (like all of gourmand frog ones) are impossible and many more (like the banana one) are very hard. There are minmax routes you can follow for them, does require some resetting though as sometimes you're just outright unlucky in the volcano or when fishing.
You also now have the option of buying walnuts. at 10k each it doesn't sound super appealing but it's really only the last 20-30 walnuts that are difficult, most of them are quick and easy. That's where your skull cavern runs come back, with some decent runs you could easily amass a couple 100k and just buy the last ones, getting you into the walnut room right at the tail end of spring.
It's definitely not easy, but far from impossible. Getting into the room well before then is something else entirely though, and even I'm fine leaving that to actual high level min-max players