It takes a long time to develop a full communication system with a horse. When you first begin the training process, the horse's vocabulary of understanding is pretty limited and that limits what you can expect of him. As he learns more, you can expect more.
Eventually there will come a time when you have developed full communication with the horse and you know he understands what you are asking. You support every request with a corridor of pressures applied consistently at every stride. Once you and the horse have reached this advanced level, you should expect compliance with every request. You do your part, and you expect the horse to do his.
But with a baby green horse at the beginning of training, we don't expect the horse to understand all of the shapes we want him to take when we apply given pressures. He doesn't understand which physical or psychological pressures we want him to ignore like the girth or something flapping above eye level. He doesn't understand which pressures are methodically applied directional pressures such as leg pressure on one side asking him to move his hindquarters in the opposite direction when we're riding or our primary line opening up for a turn when we're leading him that he can remove by taking the shape we want. We don't expect full compliance in the beginning because the baby horse's vocabulary needs to grow.
So the baby horse has to add these pressures one by one to his vocabulary. You have to break everything you want to teach him down into the smallest number of little tiny pieces that you can. Then teach each of those things one at a time.
There isn't any hard and fast rule about how long an individual training session should last when you are working the horse. I like to think of each lesson in thirds. There's a warm-up third, a training third and a cooling down third.
You spend the first third of the time in a warm up arrangement that mentally and physically gets the horse in rhythm with relaxation. If he's a beginning horse, he may just run around and play with you following him around. If he's a little more educated you might longe him or do some gymnastic exercises under saddle. This is the time when you allow him to work slow to be pumping the fluids in his legs from his frog and to get his joints working free and muscles warmed up.
The middle third of the training session is where you practice things the horse already knows and it is the only time when you introduce anything new, anything beyond what the horse already understands. You never introduce something new out of the clear blue sky. Anything new should be only a tiny baby step away from what the horse already knows and has practiced. You go along really slowly and introduce things in very small increments so the horse stays interested and the rhythm and relaxation keep going. And don't hesitate to just stop in the middle if everything turns into a can of worms because it's always better to stop and reboot.
It's important to recognize the difference between teaching the horse something and him just accepting it. For example, a laid back horse might stand there and accept the saddle pad and the saddle and the girth and so on. Because the horse is accepting each new thing as one of those things people just do and staying relaxed about it, it looks like he's trained. If you don't realize you haven't really taught the horse anything yet, there's going to be a wreck when you come to a place where the horse's acceptance and his understanding are in conflict. When you try to tell him to move and do something with all that stuff on him, that's when he's suddenly going to find that he's being attacked from all directions by something that has him restrained and constrained and his excitement level is going to go right through the roof. It's a very tricky thing because a lot of people think that a horse that you've never had to develop any control over is a perfect horse but actually they just don't have any control over him.
In order for the horse to add a pressure to his vocabulary, at some point he has to resist things a little bit and you have to calm him a little bit and show him that you're a friend he can trust not to hurt him. That doesn't mean you go around picking fights with him. If you add something new and everything's fantastic then take it all off today. Do it again the next day and the next day. After three or four days you can start heeding him with all this gear on. When he's heeding really well with all the gear on, then you longe him with it on. Then someone just sits on him. Then you heed him with someone on his back. Then you longe him with someone one his back. And gradually you add the bridle and bit pressures and you just go along baby step by horse-logical baby step.
The last third of the training session is the cool down period. This is the horse's time to physically and mentally unwind before you put him away. If everything's gone along great, you've practiced the things the horse already knows or added another little thing to his vocabulary while keeping him rhythmic and relaxed. The time to start cooling him down is while everything is going well, before he gets tired or his attention starts to wander.
Any time you're having a good time and it starts to change, that's the time to cool him down and put him away. Any time that the relationship between you and the horse seems to be going the wrong way--he's not interested in you today or whatever--you let him play a while and then put him away. Any time you're not sure what to do next, that's the time to put him away. Any time you feel you were lucky and got away with something, that's the time to put him away.
The horse's daily training routine should not be based on a set of particular actions you've decided to take to teach him according to any particular schedule. A training routine should be based on the horse's reactions to your actions. A good routine maintains both the horse's comfort level and the horse's attention level.