I had to go back and look at this one but your right, It already does have a data file, I was wrong lol. I haven't messed with this one in some time I was thinking it was something a bit more simple but like my other plugins I left room for improvement and your suggestion might can work.
The 24 hour delay or timer will be the trick. I have to be able to either tell the system to run the command for each player after xx seconds (or 24 hours) when they log out which requires a timer to be set when the player logs out or do a random scan every xx seconds for sleepers that are outside with a timestamp longer than xx seconds.. The random check every so often would probably be best for system performance