Er... Was STB abolished somewhen? Then... Why does it have to return?!?
Well, on topic: Active Battle Time means every participant in the combat has a bar that fills up. When it maxes, it's your turn. You can give orders and the char will carry 'em out, then his bar will be flushed and recharge again. While you give orders, time runs on. Means it lacks the action of realtime battles while not having the time to think about tactics like in turn based environments. It really sucks, especially when the menues are five levels deep and have like 8 pages each. In FF8 you wouldn't use magic because it'd take like 10s just to give the command and the spells' strength stood in no comparison to the time needed. If they're smart enough to make the game pause while you give orders, it'd be more acceptable, but it's not likely to happen.