I build my round up last year doing weekends. I had to work 7 days a weeks, PAYE job in the week and my own business on the weekends.
its hard work, I found you can keep working for about 2 weeks straight before you need a day off, otherwise you burn out.
the trick with the switch over, (if you don't have a choose, money wise) is once you have about 200 customers is to negotiate with your boss to take one day a week off (preferably Friday's)
then continue to build till you can go full-time.
I think you could do longer than 2 weeks bud.
I did 6 weeks solid a few years back, tired yes, but could've done more if needed.
Guy I heard about works in a garage (flogging motors, not selling 'em) he did 363days in a row year before last. Boxing Day to Christmas Eve. I never did find out why.
I don't think that's doable as a proper job though.