Very feasible with day trip. You can sleep on way in and out. Day trips offer 3 dives but in my experience only 2 on the wreck that you can do as 1 long deco dive if you want to and typically 1 at Ras Mohammed.Everyone I know who dived Thistlegorm did it from Sharm and had to wake up at 4am and were gassed by the end of the day. It is best on liveaboard to cut the travel time.
I probably have 15h on it and would do a day trip any day to go again.