I am sure that this is an individual thing. But my supply did not take a hit when I returned to work at 2.5 months. In fact, I thought I should be pumping 3x/day based on when Maya ate, so that is what I did my first week back. I WAAAAYYYYY overproduced what she could drink and I also leaked all over the place that weekend lol! Mostly because Maya was a one-sided eater and I was pumping double - so I basically pumped twice as much as I needed. So, just using that story to illustrate that your supply won't necessarily take a hit at all. I went to 2 pumps a day and was still overproducing up until about 6 mos when my supply regulated and I just pumped what I needed for the next day. I think if you are lucky your boobs will get used to the teaching schedule and you will be able to pump all you need with your two pumps - morning and mid-day.
You may get full and uncomfortable during those first long periods without pumping, so I would wear nursing pads in your bra just in case of leaks.
As you suspected, there's no definitive answer, depends on your body.
However, given that you're going to be ~8 months PP, your supply should be pretty well regulated, and hopefully won't be too affected by only pumping once before work and once during.
*SPENCER* happy Mami of two precious princesses!
Hmmmm...here is my plan, perhaps it needs tweaking as I was thinking of using my freezer stash.