WR, what helps my endurance and you can do this in about 20 min. a day. I don't know if you are familiar with Indian history or not but one way to move a war party quickly from one place to another was for the trail member to sprint to the front of the line and then sloww the pace to the rest of the party. And then the new trailer would repeat the process. This being done to quicken the party and not tire them out. Hence the Term "Indian Run" Whew....Now on to what I was getting at, Seince I doubt you will be doing it the way explained above, start by running at a moderate pace, every other telephone pole sprint, then jog the next two, pause and do PU's about 40 or so(also a nice break if you are winded), then get up and sprint the next gap and repeat, sprint 1, jog 2, PU's and repeat.
If you stick to it and drink plenty of water you will notice it in your riding after the first week or so.
Good Luck,
Phillip