The idea is to get to the checkpoint and not be last.So them who finished 25 hours ahead, will get that headstart on the next leg? Im sure a similar thing happened on a previous episode/series and that didn't happen and i remember thinking it was unfair?
In the last 2 series, they all left the checkpoint staggered by the times that they arrived. So if couple one arrived 25hrs ahead, they leave 25hrs before everyone else.
The couple now ahead can afford to stop for maybe a day and do some work to top up their funds.