Revelation Online details the fine points of aptitude

[AL:Rev]You’ll earn experience by doing a lot of things in Revelation Online, but don’t you wish that you could earn more experience for doing the same things? That’s where Aptitude comes in. Aptitude is a constantly renewing resource, with characters receiving a certain amount of Aptitude on a daily basis, allowing for additional experience gains so long as there’s more Aptitude in reserve to be used.

What if you can’t log in for a bit? Well, your Aptitude continues to accumulate, and any “overflow” accumulated is stored by an NPC who will sell you that banked Aptitude, up to a daily limit. You can also purchase even more beyond the daily limit, but that will cost you. So you can catch up if you’re unable to log in for a little while or you can just enjoy the daily fruits of your login labor. (For a very generous definition of “labor” here.)