let me know when

[azz]

a. We'll have to talk about this. Let me know when is a good time.
b. We'll have to talk about this. Let me know when will be a good time.

c. We'll have to talk about this. Let me know when it is a good time.
d. We'll have to talk about this. Let me know when it will be a good time.

e. We'll have to talk about this. Let me know when it is a good time for me to call you.
f. We'll have to talk about this. Let me know when it will be a good time for me to call you.

Which of the above sentences are grammatically correct?

Many thanks

[Alan]

Correct/most natural: A & E

Others: unnatural, although comprehensible