I hate to be the bearer of bad news but people do not solo in 8 hours anymore.
there are of course exceptions to every rule just like there are 24 year olds flying for CAL but it is rare.
those who solo in 8-10 hours are typically in piedmont north dakota on a one runway uncontrolled field flying a cessna 152 AND have exceptional pilot skills and a great instructor.
I have over 800 dual given now and the best I have seen is 18 hours. Granted I think that is a little high but you also have to take into consideration as was previously mentioned that it depends on alot of factors. I instruct at the second busiest airport in New England 9 miles from BOS and it does take easily 20 minutes from start up to take off not to mention being extended on downwind every single run around the patch which eats up valuable time. Couple in with the fact the communications and all of our planes are newer SP's with GPS and autopilot you have a recipe for a few more hours in the logbook.
I just simply put have alot more that I need to teach a student and they need to digest at KBED than someone in a different environment.
It is not a race and it is just a question an instructor can not answer. "how many hours until I can solo?"
I have done what was mentioned earlier in some instances, if they were competent pilots but not quite ready to kick me out we have just moved right into the navigation and honing of their skills and they have then gone on to do their first solo on one day and then their first solo xc the next week, I have seen positive results from that.
Its a marathon not a race