See how you feel when you get further along stargazydrifter you might want to leave early, but then would that mean going back sooner? It's a hard choice, and one I'm so glad I didn't have to make, but I know a lot of people who found going back really hard and wanted to have as long as possible.
I'm not sure what you do, teaching little people did get hard towards the end, I had great support staff who did a lot and I only worked mornings towards the end, but it was exhausting. I would sleep all afternoon when I got home. There was a point to this....oh yes, there are probably other options for you than taking leave early, cutting back hours or using annual leave to shorten your week. It's worth talking through options with your work place!