In a G-reg you need to do 3 takeoffs and 3 landings, all during official UK-CAA night (official sunset + 30 mins).
They need to be done
either with an instructor in the RHS (who himself needs to be night passenger current, or hold a valid JAA IR which exempts one from the 90 day requirement)
or with nobody else in the aircraft.
In an N-reg the rules are slightly different, and the 3+3 need to be done after sunset + 1 hour. Night flight is logged after sunset + 30 mins (the 30 mins is actually an approximation but is widely used) but the night passenger carriage renewal needs ss+1hr.
I hope I got all that right
