When not to wake a sleeping baby

Hi! FTM here and EBF. My son is almost 3 weeks old and boy, can he sleep. He is almost impossible to wake up. When I was at the hospital, the nurses told me to wake him every 2-3 hours during the day to feed and let him be during the night unless he cries. He is doing great and is gaining lots of weight! Is it okay to just let him sleep during the day now? I feel like, because I'm waking him every 3 hours, he is stuck, like clockwork at night every 3 hours.