I miss the days that I was trouble-free.

I know it would be correct if "that" is replaced by "when," but can "that" also be correct?

Also, I have this faint feeling that there are two types of clauses that denote the time of occurrences, one in which no "that" or "when" is needed (the day she left), and the other type in which "when" is necessary (the days when I had to walk home alone after school). I think in the first type, the action described is often transient, whereas in the second the action usually spans a period of time.

I'm confused and didn't find the answer after several searches.

Any help would be appreciated.

In this sentence:

I miss the days that I was trouble-free.

I know it would be correct if that were replaced by when, but would that also be correct here?

Also, I have this faint feeling that there are two types of clauses that denote the time of occurrences:

1. one type in which neither that nor when is needed
   (e.g., the day she left), and
2. the other type in which when is necessary
   (e.g., the days when I had to walk home alone after school).

I think in the first type, the action described is often transient, whereas in the second type, the action usually spans a period of time.

I’m confused and didn’t find the answer after several searches.

Any help would be appreciated.

I miss the days that I was trouble-free.

I know it would be correct if "that" is replaced by "when," but can "that" also be correct?

Also, I have this faint feeling that there are two types of adverbial clauses of time, one in which no "that" or "when" is needed (the day she left), and the other type in which "when" is necessary (the days when I had to walk home alone after school). I think in the first type, the action described is often transient, whereas in the second the action usually spans a period of time.

I'm confused and didn't find the answer after several searches.

Any help would be appreciated.

I miss the days that I was trouble-free.

I know it would be correct if "that" is replaced by "when," but can "that" also be correct?

Also, I have this faint feeling that there are two types of clauses that denote the time of occurrences, one in which no "that" or "when" is needed (the day she left), and the other type in which "when" is necessary (the days when I had to walk home alone after school). I think in the first type, the action described is often transient, whereas in the second the action usually spans a period of time.

I'm confused and didn't find the answer after several searches.

Any help would be appreciated.