The USCG describes 1 day of boating is a minimum of 4 hours.
That means 4 hours boating in a single day logged = 1 day
That means 8 hours boating in a single day logged = 1 day
That means 12 hours boating in a single day logged = 1 day
NauticEd might be a little more flexible in that we want you to be experienced and accomplished and competent so maybe if you went out for 3 hours today and 3 hours tomorrow, we'd probably allow that as 1 day total whereas the USCG would technically say none.
Ultimately, we believe that experience combined with theoretical knowledge and skills training makes you competent so we are not sticklers on the details but we are on making sure that you know where the line in the sand is - no cheating the system - be honest as possible - do what is logical.