Calendar year 2019 990 extension is due July 15 2020. Fiscal year - 15th day of 5th month after YE, unless that falls between April 1 and July 15 (or something like that), then July 15 

I dont prepare 990s but in all the other types of returns, you need to check a box at the top of the extension form to Freeze the amounts flowing to it, so that you dont get errors about missing info....does the 8868 have a box near the top of the form for this?