I have some left over wallpaper border that I want to use to replace some areas that my 2 year has rip?

Question

but I can't remember how long the pre-adhesive borders are suppose to stay submerged in water.

Answer 1

15 seconds.

Remember the patches may be a different color than the one on there already.  Environment changes the colors of things, but your patch has been protected from this type of thing.

Answer 2

just a few minutes, at least the ones i used were like that. more or less just long enough to make sure its really wet, but not so long that the paper border gets ruined.