Had I a 3 year old, if I sent it to the trainers, first of all it would probably be for 30 days only just to get it broke, after that I would prefer to do all the rides on it myself. Following the trainer I would probably work with the horse 4 days a week, walk trot and minimal canter about 30 minutes a session and chuck it in a field for the winter (4 to 6 months). In it's 4 year old year I would be riding it 4 - 5 days a week for 30, working up to 45 minutes, starting around now to get it ready for showing this year. By May I would hope to have the horse putting together a solid training level test, and working on the FEI 4 year old test stuff like lengthening the stride, yeilding from the leg, sitting trot.
Thats my personal opinion though, and only barring any health issues. Young horses have such a short attention span I find it hard to keep them away from their buddies for more than an hour or an hour and a half including groundwork and grooming (unless of course they are having "issues" requiring a "tune-up" in the form of a frothy bum and a wet saddle pad :P) so I don't like to work them for a long time just kind of walking and trotting around. I like to do stuff with them, mini hacks, poles, transitions, transitions, transitions and if they are apt to something, like a lengthen stride, then develop that. I might do like 2 20 meter circles in a row, max, and after that it's onto something new. I also prefer to keep them on a consistent schedule, 5 days a week seems to work well with short sessions rather than one marathon session a week.
I would not be expecting to seriously school second level movements until December or January when they are 4 as they do require muscle strength, coordination and some "strength" in the joints which would not be developed at this point in their training. After a good 6 months of consistent riding, 5 days a week, I would start asking for baby shoulder ins, travers, and start working on the walk-canter and collecting the canter in prep. for the canter-walk.
Hope that gives you a decent timeline... There was a great article in Dressage Today about how this one guy gets his horses going and it was great to read. Obviously add like 200% of the timeline from his hahaha as he is a serious professional with these horses!! It's crazy how fast he can get them out and about. I think it was like 2 months from unbroke to horse show...
There is also a great Klimke book about young horses... I have it somewhere.. it's quite realistic and gives some great ideas about what to do with your babies.
They say money doesn't buy happiness -- well happiness doesn't buy horses!