Help with a weekend slump in meditation practice

On work days (5 days a week), I'm normally able to get in around 4-4.5 hours of meditation a day, normally walking and sitting for 45 minutes each and then some Anapana meditation usually at the start and end of each day. On the weekends, I usually am able to do the same sort of practice but around 8-10 hours worth. Curiously though, on the weekends, it seems like my practice takes something of a slump, if it is even that. Towards the end of the day on weekends the pain that normally arises in my leg and I am normally able to be mindful of becomes exceptionally more intense, to the point that I'm sometimes only able to sit for 30 minutes. I know the length you sit isn't so much important as how mindful you're able to be; I guess what I'm trying to ask is, how should I reflect on this, and also how should I judge the "progress" of my personal practice in general? Thank you