Exmark has a productivity chart that I've used for years. Exmark Mower and Equipment Productivity Charts
A few things to keep in mind:
1. The Toro Timecutter is a residential mower so you can't cut as fast as the commercial machines. So, for weekly mowing figure around 4-5 MPH on average. (spring slower - summer faster)
2. Use the 80% number. Most of us typically have a little overlap when we are mowing stripes and this also figures in spots where you can't take a full-width cut.
3. Don't discount landscape beds unless they are huge. That area you are not actually mowing will compensate you for loading/unloading equipment, blowing grass off the sidewalks, and string trimming.
4. The chart is in acres so you will have to convert that to sq. ft.
5. If you have commercial clients with multiple locations add in mileage (travel time) from one location to the next. If you perform excellent, no-hassle work they won't mind paying you for the entire job.
So, your Toro Timecutter 50-inch will mow about 2 acres an hour at 80% cut. (87000 sg. ft.)