The current system is a bit thin.
I understand it is in place to make sure sitters don't abuse another account and technically use it as a dual account, but now the accounts of working people without much time to login are way behind.
What I suggest is to either be able to set the 15/30 days for each sitter (and after the 15/30 days another sitter can take over).
Or, extend it to 30/60 days. It'll be just a bit more over half the server duration, and the accounts with lesser active players can still contribute to CC's or the end game.