Wanted to share my experience. Flew BA127 LHR-DOH landed at 23:15 towards C gates area but no train. Immigration, baggage and recheck was easy and I was back airside within 30minutes. While I have OW Emerald status I didn’t use fast track for either immigration, checkin or security so the only benefit was priority luggage. The main factor I believe is many arrivals are post midnight that may slow down immigration and baggage. Connected to QR 1369 2:10 departure and managed decent lounge time.