For 75’s, I would start with 25s rest. When you can make all (or close to) 30, lower your start time to 20s rest. Then you work towards lowering your goal time with the same start time until you are at 25s rest again. Rinse and repeat.
For 50’s, the same but 20s towards 15s.
Got it! We'll have a look and get back to you ASAP!