It took me about 6 months before I could live on the money - and my outgoings were very low back then. However, it started slowly for two main reasons. I started in October (1991) and many people were paying 15% on their mortgages back then - plus there was a lot of unemployment (the very reason that I started window cleaning). Things accelerated after Britain pulled out of the ERM and interest rates plummeted.
I took about two years before I regarded my round as full. However, I could have done it much more quickly than that as I didn't need a full round in order to live.
The first six months were a bit tough but I supplemented my income by going away one week per month on a self-employed driving job. That slowed down the canvassing too.
So it's hard to give a straight answer because the economic pressures were different back then.
However, I reckon that two new customers per hour of canvassing should be comfortably attainable. So let's say £30 per 6 weeks per hour of canvassing. 100 hours of canvassing should give £3,000 per 6 weeks. 150 hours of canvassing should give £4,500 per 6 weeks (if offering 6 weekly). By canvassing, I mean after 5 PM when more people are in. So, say between 5 and 7.30. 2.5 hours of canvassing per evening means that £3k a month turnover could be achieved after 60 weekdays (Mon - Fri). Obviously weekends can be longer days.
There will be referrals and people who see you working who will ask for quotations. There will also be expenses - generally much heavier at first.
All of the above assumes that the world grows in straight lines. There will be customers who drop you after one or two cleans, others who drop you after 4 or 5 and others who mess you about so much that you drop them once you can afford to.