I need to send in 2018 still. After I mail those tomorrow, when can I try to e-file my 2019?

[xmasbaby0]

Any time you want to.   There will not a a 2018 AGI in the system for you so try using zero for the 2018 AGI.  If zero will not allow you to e-file 2019, you will hav to print, sign and mail 2019.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.