intense jumping session; 10 mins, flat work; 2 min long rein trot (loosen up base of neck) and 10 mins walk. Long rein trot makes a huge difference to encourage your horse to hold their own contact and use their whole body :)
They usually say that 10-15 minutes of walk on a long rein should be enough. I do not say it is not right, but it depends on so many factors. I always walk for 10 minutes continuously, stop, feel the breath, look at the nostrils, if they are still enlarged... if needed, we walk for some more minutes. I sometimes loosen the girth by one hole too, just that the horse gets a part of the reward in advance.
I ride everyday except for Mondays, 2 times a week jumping.
If your horse is generally fit and in full work, you shouldn't need to make a point to take long breaks in between exercises during your ride. I use walk breaks as a reward when they do a good job, and then it gives us both a minute to catch our breath.
For the end of your ride, I usually look at a few things to decide if my horse is cooled out enough to stop walking them. If your horse is visibly puffing and breathing heavily, they are definitely not cooled down. If your horse's chest is notably warmer than the rest of their body, they are not cooled out yet. If they are still really sweaty and wet, they may also need some more time before they are done walking.
Sweat isn't the single best way to decide if your horse it totally cooled down. If you have a horse who naturally sweats a lot, or if they have their winter coat, they may not dry off as quickly as they stop breathing hard, etc.
i say to trot for a good 5 min straight without asking for much, maybe even on a nice relaxed loose rein. than wail for a good 10-15 min after again nice a relaxed. something i do if it's really hot and the sun is coming down on you and your horse go on a trail ride or walk around the property in shade to cool down. i also recommend to hose the horse of with luke warm water and graze until your horse is completely cool. :)
I would say that after a big session 5minutes of trot reins pretty supple and 10 minutes of step by letting the horse stretch is a minimum. After a trotting, I think that 5 minutes of step in the saddle and then 20 minutes of step and of grazing in hand is necessary so that the horse finds its breath to 100%, because the trottings are generally quite long and the fact of making Trottings outdoors excites the horse more !! For a workout on the basic dish I think 10 minutes of not long reins are enough. After all depends on the horse and its ability to regain its breath some need more time to regain a good heart rate.
Have a good day :)