i have a full time job, always have but i work shifts so i fit my windows in around that, my full time job is an electrical mechanical maintenence man 
I did some security work when I first started window cleaning (oh and I also worked one weekend humping bags for Royal Mail which was an eye-opener; but I seriously couldn't hack doing that for a living), and I found it tough trying to fit window cleaning in with another job.
I was permanently knackered, though much of this was down to my inexperience as a window cleaner.
Don't you find trying to work window cleaning during what should be your 'rest time' demanding?
to be honest tosh, no, if i never had other work i would go mad, i am a bit strange in the fact that i love working, since i was 16 years of age i have had 2 job,s , only time i never was when i was a lift engineer as i worked away a lot. I regulary do 14 hour days some weeks and feel great, my shifts allow me to spend more time with my son as well because i only do the windows when he is in nursery so i would therefore just be sitting at home. i work a 3 shift rota of Lates earlies nights. never feel tired even if i only have 4 hours sleep.

. got another kid coming in june so it may all change
