What an awful schedule!!!! Dumping an additional 200+ badly jetlagged passengers into MAN at the same time as the other arrivals from Asia and US
06:05 actually makes this one of the earliest long-haul arrivals at MAN, and given that such flights usually arrive upto an hour early the pax are unlikely to find the main body of US/Asia arriving pax queueing alongside them at immigration. Only Thomson and Thomas Cook have [some] long-haul flights scheduled to arrive at MAN earlier than this, and Hainan will share a terminal with only one of these carriers. So whilst I sympathise with your desire for an evening schedule for other reasons, I don't believe that Hainan pax arriving at MAN will hit peak-period for queues. Transit through the airport procedures should be as painless as it gets at this hour.
Note also that these timings do work particularly well for onward connections via MAN. Could be very useful for some.