You would signal move up and indicate a depth.
I have been taught to indicate move up with a hand flat facing down and moving upwards, but in a half circle towards me. you should discuss this before the dive as I don’t think it’s a signal that everyone does the same way or know.
Move up in one minute to 18m would be:
- One
- Move up
- 1
- 8
- Then OK to ask my buddy to OK me back
Once you are there just signal that you are doing x minutes stop.
I don’t think there is a signal for deep stops. Whether you want to do deep stops or not is another topic.