It must depend on a number of variables such as previous experience, continuity especially, quality of instructor and individual aptitude.
Flying every day in good weather with a good instructor will get you solo much quicker than flying once a fortnight in the winter.
When I did my training most of us went solo in 7-12 hours. Much longer than that and there was a training risk for later in the course, and it would be difficult to complete the course in the prescribed hours too.
I agree with B73 that it is not a factor in the great scheme of things, but would also say that someone who struggles to go solo will probably also struggle later in their training, and it may be better to cut their losses early (if the school doesn't do it for them.) Difficult, I agree, especially if you are paying for it yourself and are desperate to fly.
There was a very sad, avoidable accident that happened about 16 years ago in the SE England. The Pilot had been 'chopped' from a commercially sponsored course and then managed to obtain a CPL by self funding at another school. He was then taken on by a North Sea operator but was again 'chopped' during his conversion phase. A small operator took him on as a pilot and sadly he crashed while doing a charter with passengers.
The point is, that it is true not to be too hung up on time to solo, particularly if continuity is a problem, but there will come a point where it becomes a falsehood to keep throwing money attempting to go solo as this is only one small step in the whole process. It doesn't get much easier after that, I would suggest.