Agree with Dan and
ANSA , I've not had a clearance to descend 20 minutes prior to requiring it. More likely about 5 mins 99% of the time, and occasionally, one needs to remind the friendly ATCO that it's time.
A colleague inbound to Darwin, in a former life, whistled over the top of Darwin at circa 10,000' in a bandit once. He was waiting to see when he'd get a descent clearance.
Hey 
you still up there? 