I was trying to find the service manual for that charger, but don't have it in my computer. I know the older version claimed a 2.5 to 3 hour time for fully charging the battery of a TK-5210.
Unless you are draining the radio battery down all the way, or using the radio frequently, your setting is probably sufficient. You could extend it to 3 hours and be sure the battery would fully charge.
The charger is smart, and shouldn't overcharge the battery. I've seen people leave radios/batteries in those for weeks at a time.
Usually the bigger concern is ambient temperatures. If you are somewhere that it gets really cold, the battery may not charge, or if the battery is really hot and the interior of the vehicle is really hot, it can delay charing.