I am not really sure when to use "a time when" or "the the when". Would someone make it clear for me?

1-At the time when I was shepherd, one could only see wolves with binoculars.

2-This is the time when I'm finally able to relax.

3-There used to be a time when I loved my mom. (Isn't she or he talking about a specific time?)

4-Anna Akhmatova lived at a time when poetry mattered.

I am not really sure when to use "a time when" or "the time when". Would someone make it clear for me?

1-At the time when I was shepherd, one could only see wolves with binoculars.

2-This is the time when I'm finally able to relax.

3-There used to be a time when I loved my mom. (Isn't she or he talking about a specific time?)

4-Anna Akhmatova lived at a time when poetry mattered.