There was of course the Pembrey FW190 which landed on 23 June 1942, so there would have been plenty of time to fly that too. It is always possible that there were American pilots at RAE flying the aircraft as a matter of course.
Ultimately we need to see the aircraft logbook for the captured FW190s, to know when they were flown by Americans, but this link entitled 'Captured Butcher Birds'
Atelier Kecay: Captured Butcherbirds - FW-190
includes this statement:
The first Fw 190 in the US was a G-3 Wrk. Nr. 160043, which arrived at Wright Field in August 1943
This is a youtube video of some captured aircraft being tested, and has quite a lot of written info too:
YouTube - Captured German Aircraft