I have two ideas:
1) Use call _getkey. Dont put any "cp KEnter" or any other conditions after,
just continue with code. This would pause it untill somebody pushes a key.
2) Do a little loop like this:
ld a,1
loop:
inc a
cp xxx
jr nz,loop
more code
and adjust the "xxx" to be whatever number would give you the right time.
HOPE THIS HELPS