I don't like to let my batteries set full for more than a couple of weeks.I usually fly weekly which means my batteries are usually only a week at most on a full charge. If you don't have a charger that will set a "Storage" charge, then just let the batteries set after you use them until the day (or night before) your ready to fly and top them off.
Letting a fully charged lipo sit for long periods of time will degrade the battery and in turn your flight times will drop off significantly.
I'm sure others will have some thoughts too.
Good luck,
Jafo