Talk:Underworld Tower to Heaven/@comment-2602:304:CE7C:1400:E9F0:2B37:24F3:4E68-20170809185615/@comment-16682378-20170810005921

^ no it won't.

If you have 4 runes & stop at screen showing what rewards you get after the Rune Boss battle, lock the screen, come back when BP is full -> you will get the Rune & enter Rune Time once you enter the tower screen again. It even works if the app restarts when you come back.

(Remember that all Rune drops from Rune bosses isn't 100%, it's still a chance drop.)