It’s difficult to say because I’m not sure of the boundary of the treatment area or how fast your electrologist works. In any case, my estimate would not mean much for your electrologist since we all work at different speeds. She might be slower or faster than me.
I can use the image you provided as a very rough guide. Just to treat the hair from the obvious treatment line halfway up the upper arm all the way to the raised t-shirt line, not including anything on the other side of that arm or the other arm and shoulder, I estimate around two hours of work just to treat the hair that is currently present.
If we can completely clear the area every two to four months, the working time should reduce by 30-50% each clearance in my experience. You could do the rough calculations for total hours required by looking at the entire treatment area and comparing it to the area in your photo, but this would only give you an indication of how long it would take me personally to treat you.
In cases like this, I would anyway recommend starting with laser since the hair density is already so strong and you’ll likely see a very decent reduction which would save you a lot of money.