After you exercise? It depends. If its the morning, get up and go to work. If its night, go to bed. Seriously though, what exactly do you mean?
In regards to cumming, i would recommend NOT. You do not want to teach your dick that Penis Enlargement time is playtime. Unwanted erections during stretches for example will only slow you down a lot. However, if you do decide to cum, anecdotal evidence suggests it will do your growth/recovery no harm.