Backing a 4 year old - how long?

I would say its possible to get the basics done in this time, however, I wouldn't expect or want any serious schooling work to be done, simply because it would be too much at once for the horse. It seems like you understand this as by the sound of it the work you have already been doing you have been taking it slow and building it up, which is the best start you can give your horse so well done for that.
The idea of sending them away is to give you the basics to work with, so you can then build on everything when they come back.
Keep things going the way you are doing, because in return you will get a fabulous horse who will want to work for you rather than you having to make him!
 
Hum. Well I am taking delivery of my new horse (four year old) in a few weeks, and am planning on taking 2-3 months to back him. The process will be:

Schooled to the voice commands on the lunge.
Introduce long reining & progress to school figures in walk & trot
Introduce in hand work to help collection & teach horse how to respond to the bit

THEN back him when he's mastered all that. It takes time for horses to develop muscle. The longissimus dorsi is the main muscle which supports the weight of the rider, that needs at least 4-6 weeks of ground work in order to strengthen sufficiently, IMHO.

Mind you, my horse will be doing some serious dressage with any luck when he's old enough, so the most important things to me are his muscle development, confidence, obedience and understanding of what is being taught. If you just want to hack about then maybe you could shorten the process a little...
 
newrider.com