according to the info i read on the back of my can of undercoating, it only takes 10 minutes. I'd give it a 1/2 hr myself.
Short answer, NO you do not NEED undercoating.
It will depend on how much undercoating you are wanting to rubberize.
how long does roof cement to dry
No.
how long does it take for bituman to dry outside
It takes about 30 minutes to dry !
40 days
An hour
time!
you will never know
is a scinentific method
Yes it does.