You DEFINITELY don't need to do 50 of them. I don't believe anyone would do 15-25 minutes of true power workouts where you are building max speed ability. 6-9 repetitions with FULL recovery is more than enough. The perceived exertion for these workouts is 20 or I couldn't go any harder. These workouts are very hard on your nervous system as well as they tax your brains ability to make your muscles fire as well.

IF you are talking VO2 max intervals where you want to work on anaerobic endurance, you would probably want to start with intervals at the top end of your aerobic capacity with equal recovery. I would do something like 3-4 minutes with that much rest. As you become fitter and more used to doing efforts at this workout you can shorten the rest between intervals. This will work on your ability to buffer lactic acid while at maximum effort but is not going to work on your absolute maximum power. These workouts are about an 18 on the 20 scale of exertion or this is the hardest I could go but if I rest I might be able to do another. At the end of this workout you likely couldn't do another. These work on your anaerobic endurance. With these intervals you could do up to 30 minutes but as you decrease the rest I would also decrease the amount of actual work that is being done.

Doing all out sprints of 30 seconds or less will create a lot of muscle damage and you should be VERY tired. It is okay to do that this time of year because it doesn't matter if you are tired because you are not racing on the weekend. These workouts are also good when you are peaking for an event where you need to be able to sprint, like a bike race. For a triathlete, these workouts will help build your maximum power IF that is your limiter.

As I have tried to point out, between 30 seconds and a minute your body changes energy system to perform that work. Two different workouts at 100% effort exist between 20 seconds and one minute. I would strongly recommend doing less than 10 of those intervals that are less than 30 seconds AND I would recommend doing a lot of recovery after them.

When you go up to one minute the workout becomes less taxing and you can do more but at that point you have a different goal from that workout.