Yep, my rule of thumb is that fully charged packs will be close to 1.5V per cell (no load). So if they're close 6V, they are probably pretty well charged up. Putting them on the wall wart is the safe way to go, though. They will probably stay cool if they are charging, and get slightly warm if they are already charged.

If you're using wall warts, buy a cheap lamp timer and set it to come on/off for one hour per day. When you put a discharged pack on it, turn it on and set the dial to cut it off in 18 hrs or so (the time-of-day setting on the dial is not important). After that initial charge, the timer will charge it an hour a day to maintain it, and you won't have to worry about taking it off the charger.