If you want to make progress in your training (and the horse's fitness) then a consistent program is vital. 5-6 days a week is ideal, 4 days minimum. I would start with 60-70% ground work, 30-40% ridden work, then slowly increase the amount of ridden work as the horse's fitness improves. Keep sessions short, simple and to the point, no more than 45 mins total work time (not including rest breaks). Each session should build off what was taught in the previous session, but avoid drilling the horse. Once the desired response is achieved, reinforce it a few times then move on to the next step. I tend to give 5 min rest breaks every 15 minutes because I find the attention span of young horses is fairly short. Sometimes I will even put the horse back in the stable for 10 mins to eat hay and have a drink before continuing, especially if it's a demanding session or a hot day. Giving rest breaks seems to help the horse stay mentally fresh in the arena, reducing frustration in both horse and rider. They're babies and it's unfair to expect them to concentrate for a solid 45 mins right off the bat. As they get older they will be able to concentrate for longer periods, but to begin with I'd give a break every 15 mins. Also it should go without saying, but be sure to include fun activities as well. Whether it's taking your horse for a gentle hack with a quiet companion, or letting them pick grass in hand, it's important to give them a break from the classroom.