Can #1 mean each of a,b or c?
1) Tell me when you are entering the pool.
a) When you are entering the pool, tell me that you are entering the pool.
b) Tell me when you will be going to enter the pool.
c) 'entering the pool' can be a habitual action, in this case it means tell me that when you are entering the pool every day
(a) and (b) are both possible interpretations, but if (b) is meant then it is a bit clearer to say "Tell me when you will be entering the pool". Your wording of (c) does not exactly make sense, but if you are asking whether (1) can mean "Every time you enter the pool (every day, or however often it might be), tell me at that time that you are entering the pool", then the answer is yes, in the context when it is understood that the person does this regularly.
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(a) and (b) are both possible interpretations, but if (b) is meant then it is a bit clearer to say "Tell me when you will be entering the pool".
Your wording of (c) does not exactly make sense, but if you are asking whether (1) can mean "Every time you enter the pool (every day, or however often it might be), tell me at that time that you are entering the pool", then the answer is yes, i