Another good one is to time yourself on the first repeat and then try to keep your time on the next repeats the same. This really requires pacing and dropping your speed on the first one.

Practice standing for 15 seconds at a time, then 30, then 45, etc.

And the idea of doing as many as you possibly can - and then one more - is fantastic. That's one of the things I do when I do these drills with a group I am coaching.