22 inch or 30 inch walk behind mower?

I currently have a 22 inch self propelled mower that I use in my lawn business.

Will I really save a lot more time by using a toro 30 inch ?

I use my zero turn mower mostly,but I do have a few backyards that I need to use my 22 inch to mow.

If a back yard takes 30 minutes to mow with my 22 inch, how much time will I cut off by using a 30 inch?