Waking in the night but not crying

Recently we moved LO to his crib in his own room overnight, as he had outgrown his bassinet and was rolling over. He is 4.5 months. He has been napping during the day in his crib since 3 months.

Sometimes he wakes in the middle of the night, but doesn't cry. Just babbles to himself or sucks his hands or feet... in the dark. Sometimes there is a few weak cries. I awake to notice on the monitor that he is awake and I have no idea how long he's been awake. I try to let him soothe himself back to sleep, but last night he was awake for almost an hour before I went in to help him. I'm afraid if he is awake too long at night he's not getting restful sleep. And as a mom and light sleeper I'm constantly checking on him.

What would you do? Just let him be, or go in to get him back to sleep?