Clean the Base as Quickly as Possible using the Quantum Mailbox and Troll Physics to Condense Time

• Start a new save for the base you want to play in eventually.
• Travel to base in front of mailbox. Mailbox is used to transfer some items between save games of same gamemode. Immediately save game and exit. Don't come back to this save for a good minute.
• Go to previous game where you can already generate fat stacks. OR...
• If you don't have a save with decent progress, start a new dummy save game and find the empty log with all the MREs along the river side opposite across from the base from where you first start at the gate. Collect as many as you can or drag the barrel back to base if you're patient enough. Sell off all the MREs for fat stacks. Repeat as many times as needed for cash. (The normal metal bucket costs like half as much as the regular bucket but Idk if it works with the mop, off the top of my head.)
• Use fat stacks to buy the cleaning supplies like mop and buckets, and a metric shit ton of garbage bag rolls. Dump as much as you can in the mailbox, maybe some extra MREs to generate pocket change too.
• Go back to your desired save game and clean the base as quick as possible with time to prep gear being skipped.

Yes, you still have to clean the base yourself sadly cause MrDrNose hasn't added an option for new saves to have a clean base, even though it would totally balance cause you skip being able to sell off all the trash bags for focusing on signal upgrades.

If anyone can find a faster vanilla method than this, or knows how to mod saves, go ahead and post it.

Edit: If you want to squeeze in even more time, adjust the settings so that the daytime length is as slow as possible and remember to set it back to normal speed once it's done. I also recommend copying the save game folder to something else in case you want an extra copy of the clean base to use again later.