How long does it take for the automatic policy builder to build an AWAF or ASM policy? busy site

There is not one fit all answer. Sometimes you can have a policy built in one day and sometimes you can wait for several months. In automatic mode, it heavily depends on how much traffic seen in a predefined period.

One important question to answer is how long does it take to see all the traffic patterns? and is there any traffic that is only seen on specific dates or events?

Beware that comprehensive mode is a pain even on busy sites, as a rule of thumb if you are not an ASM expert I would then recommend to start with a relaxed policy and as you get more traffic, you can tighten the policy up to an acceptable level.