Most of the time, my birds come out in one hour spurts - one hour in the morning, one hour after we get back from work and one hour after dinner. Sometimes, it can be up to one hour and a half, but specially since we had to split time between the littles and Léa, it's how it goes during the week.
Petey seems to have understood this concept of one hour and generally, when he feels like going for an attack (on me) he chooses to do so during the last 15 minutes of time out - it's unmistakable. It's like he knows that such an offence normally gets him a time out for 10 to 15 minutes, he might as well make his move then.
Léa seems to slowly have a grasp on time as well and the whole hour-out notion. Lately, she's been quite active and generally when she breaks rules too often, she can end up in her cage a little prematurely. She seems to have figured out a way around that - make mischief all she wants in the first half hour, start to calm down in the following 15 minutes and to be completely quiet and still, engrossed in beads or the like in the last 15 minutes, often making us forget that she's been out and possibly overlooking the time and therefore managing to get an extra 10 minute or so, until one of us realizes that it's her time to go back in her cage.