QIAdmissionController get time before grabbing the lock
QIAdmissionController get time before grabbing the lock

Summary:
Move the code for getting the current time before grabbing the lock in order to decrease contention.

This wasn't clearly identified as a bottleneck (at least not on my machine) but this is a good practice to minimize the amount of code executed while holding the lock.

Reviewed By: spalamarchuk

Differential Revision: D13660670

fbshipit-source-id: 9a06fba4d3a6d52320bb9a88720f7855d1accef8

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift