if it's a one off ew, then yes do an early bedtime. 30 - 60 mins earlier depending on your bub. (i used to just do 30 mins earlier as otherwise we got ew again, other bubs just wake up at normal time)
if his last nap ended at 3.45 and he normally handles 3hrs A time, then a 630/6.45 bedtime would probably work. (so look at the last A time needed rather than the 12 hr day in this case)
i also used to sometimes drag out bath routine slightly longer than usual (so longer bath, longer baby massage, take my time putting his pjs on, etc etc) to sneak in an extra 15mins without him getting too OT. if i let him play the extra 15 mins he would fall apart but doing it this way he didnt mind.
HTH