The first thing you need to keep in mind is your rental is based upon time measured two ways. It's calender time, one week, and hour meter time, forty hours per week. So if you work the machine twelve hours a day for seven days you are going to have to pay extra for all the hours above forty.
I've found pulling stumps fun. My first observation was that the roots aren't all created equal. So my first concern was to try to guess which side of the stump would have the weaker roots. That's the side I want to lift. Then I try to use the stump as part of the leverage process against the stronger roots.
Ideally I cut the weaker roots and then pull the stump up and out peeling out against the stronger roots. If you try to lift the stump out putting the bigger roots in a shear it takes a lot more power and work. However if you use the stump as a handle to pull the bigger roots out of the ground there's a lot less resistance.
Keep in mind the tree has designed an anchoring system to prevent it from being up rooted by high winds. Since you're working with the stump you don't have the leverage the wind has with a complete tree. So you have to defeat the design of the root system. The best way to do this is to cut one side loose from the anchor. And then pull the severed trunk up and over the remaining anchor. The anchoring system is designed to resist tension and shear. You want to attack it's weakness, compression.
Hope this helps, have fun.
