How long does it take for mailed taxes to be accepted?

I didn't file for taxes last year because I only had a net investment loss, and frankly forgot about it.

This year, after the e-file date was closed, I decided to mail in the previous years taxes. This was slightly over a month ago. Now I'm trying to e-file this year's taxes but it's being rejected, I'm assuming due to a mismatch in the AGI. Does this mean my previous years taxes are not entered into the government's system yet? 

How long should I wait?

Would it be unwise to file this year and say I didn't file last year for it to be accepted? This will create a mismatch in the AGI if they do accept both.

Will I still receive the stimulus check?

Thanks in advance.