This would mean the flight would have to depart DOH around 2 pm, whereas QR's medium and long haul flights from Europe/Africa/LatAm all arrive at DOH in the evening and overnight hours, so nobody could connect without a long stay in DOH. You'd be looking at a layover of at least 7 hours coming from LHR or JNB, and at least 16 hours coming from GRU...

Taking those connections and aircraft utilization into account, I think they would follow a schedule closer to what EK and QR currently offer, leaving Tokyo at night, arriving in Doha very early in the morning, and turning around a couple of hours later to arrive in Tokyo at night. The main question in my mind is whether they can get the plane back to Tokyo early enough to enable connections on the Japan end, because a midnight departure from HND means arriving in the Gulf around 7 AM, and then if you turn the plane immediately you can't get back to Tokyo until midnight. Whereas with access to a daytime slot pair, they could potentially depart HND a few hours earlier in the evening, so as to get to DOH a little after midnight (in time to make many westbound connections), then turn the plane in a couple of hours and have it back in Tokyo around 8 pm.