HH, as Led Zep has said, even the "request clearance" bit is superfluous if you have submitted a FP. ATC call your flight plan up the moment they receive taxi/departure notification. They know you have planned to enter CTA, and what level you want. They know you will need a clearance. You will get one when they can issue it, which can depend on the traffic, sector layout (i.e a "CTA" sector overlying a "Class G" sector) etc. Having said that, if you have to maintain i.e FL180 without being told "expect a delay for clearance", I'd pipe up.