with regular canvassing as you have described and leaflet drops as some days you wont want to canvass then probably about a year to gain 200 quality customers however you do reach a point where work starts to come in by itself like magic - recommendations / people seeing you about.
the best 3 bits of advice I can give you is
1 get signwritten with big "window cleaner" with mobile AND landline number even if its a VOIP line
www.vonage.co.uk 2 always do summit to grow canvass, leaflet, talk to friends and neighbours etc
3 if you get a non or slow payer NEVER EVER EVER EVER EVER do a second clean with an outstanding debt as you prob wont get that payment neither ...... dump em as soon as you get paid none of this dump when replaced with 2...... let them have 3 strikes etc etc just fook em off there and then and spend the time canvassing as opposed to debt chasing or more cleaning of a crap customers windows ............. a bad customer is not a customer in any way shape or form
good luck with it !!!