This is Fall year 7. I played the farm normally except for keeping large amounts of trees around. Once I had 2 medium clumps of mushroom trees I cleared everything except for the trees and mushroom trees. From that point it only took maybe 3-4 hours IRL time. I would sleep for 10-15 days then wake up and clear all the debris and put tree fertilizer on new mushroom seeds. Ended up using 776 tree fertilizer which I mostly bought through Robin/Desert Trader (buying stone, then trading stone for fiber, then crafting the fertilizer).