Great tit leaving nest for hours to return prehatch

Not sure if this is where to do this but here goes- I have a nest box camera and great tits in nest. On Saturday when it was warm- around 18C the hen who had been sitting on 6 eggs for about 11 days went away for the whole day. We were devastated thinking that she'd abandoned...... but then in the evening she returned. Yesterday, Monday one chick hatched and today there are five. Both parents are being hugely attentive. Was the hen's absence on Saturday normal pprehatching behaviour.Seems sensible as she would have had a chance to feed before the hard work really started. Anyone else seen this?