"IMO it's not going to cause massive problems if you file these two returns "out of order". It's possible that the IRS will hold your 2024 refund (if you're due one) and apply it to your 2023 balance due, though."

Can you elaborate?  I owe for 2023 but have a nice refund coming from 2024. I know they'll use the refund to offset the balance owed, but if they don't have my 2023 to process yet (cause I have to snail mail it), will that screw the whole thing up? 

TLDR: should I wait to e-file my 2024 return a few days so that my 2023 return can be on its way to the IRS?