Hi Jens,
Great questions: Resting Heart Rate is typically taken in the morning as soon as you wake up. It may not be convenient for many people to do that, so immediately before training is also ok. This just helps us establish a baseline of your current condition.
Recovery time in this instance means: How long it takes to get from finishing heart rate (in this case right after you're done running), to less than 120 beats per minute. It can also be measured to be until your reach Aerobic threshold, but that involves some calculating, our app bases the recovery time on 120 or less bpm, at the moment.
Time in between intervals, is actually as long as it takes for you to recover. If your heart rate is not below Aerobic Threshold, or less than 120 bpm, you should not move on to the next interval. That has taken 10+ minutes in the past, but it's an important part of getting the most out of your training.
Let us know if you have any other questions.