Do you wait for your baby to be crying for a feed or feed them when they get fidgety?

With my 1st child I had to strictly feed him 3 hourly to flush his jaundice out so I always had to wake him.

With my 2nd (6 weeks old) will fidget when feed is due but then go back to sleep by time I've sat up in bed etc. Then sometimes he will only drink an ounce and go back to sleep again. Wondering if I should wait until hes properly crying for it? I'm thinking more overnight to do this as day time I generally have to feed him around a routine etc.