If he is not going back into the water until after dark this could be a worrying sign. It is quite mild at present, and so he could be fooled into thinking March has come. As the weather cools down again in the next few days, if he is still out after dark I personally would pull him inside for some R&R. That would mean the end of his hibernation for this year however.
European Studbook Foundation (ESF) Studbook Keeper for:
Terrapene carolina carolina
Terrapene carolina bauri