How long / how much to pump

I work full time 40hrs + but the biggest issue is that I have a really long commute. My schedule starts with at

4:30AM

6:30AM

9AM

12PM

3PM

6PM

And home by 730 and feed LO again to sleep

Typically I pump 20+ oz a day. I think my max has been 26 oz and I still feed baby at night.

My question is for how long should I pump? I am only able to pump for 10 to 15 mins max at work per session and I feel guilty for the time away... how do you mammas do it??