You should plan for your turnover to be at least double the average industrial wage in your area,.... because after tax, equipment & running expenses you're only left with half! So if you can't meet that target you'd be better off in a "real job".
As mentioned previously, there is a lot of down time in this industry, due to weather, equipment & vehicle problems, sickness, and simply the time it takes to run a business like invoicing, paperwork, meeting the accountant & running to the bank etc etc,.. it all takes away from time spent on the glass. Plan to work 5 days a week but plan to earn enough to survive in just 4,..