That's not quite correct, ck, as 'night' is defined as follows:You supposed to use lights after sunset till at least sunrise, assuming he started out earlier he was was riding before sunrise unlit so you can effectively tell him he was breaking the law..
https://www.gov.uk/rules-for-cyclists-59-to-82/overview-59-to-71
Night (the hours of darkness) is defined as the period between half an hour after sunset and half an hour before sunrise).
Laws RVLR regs 3, 24, & 25, (In Scotland - RTRA 1984 sect 82 (as amended by NRSWA, para 59 of sched 8))