I recently did my 300 NM cross country flight here in Spain. The way I had to certify it was getting a stamp on a piece of paper from each airport where I took-off and landed for both a Departure and Arrival column and then stating the distance flown between the airports. You then fill in the date at the end of the sheet and sign it...so basically there's no way to know if you did fly it all in one day or not unless you check it with the logbook.