About 20 minutes.
. . . but T had other ideas. Time for daddy to go to bed was obviously also time for baby to wake up, so (apart from 5 minutes dozing off here and there) it was 12:40am (two feeds totalling 130ml and one nappy change later) before any decent sleep was had. Mum slept through most of it, which may be why she took it upon herself to do the early morning shifts (although I still had to get up to lift the baby out of the crib).