Times when only small letters will do (5)

'times' is the definition.
The answer and definition can be both related to time as well as being plural nouns.
Perhaps there's a link between them I don't understand?

'only small letters will do' is the wordplay.
I cannot really understand how this works, but
'small' could be 'wee' (similar in meaning) and 'wee' is found within the answer.
This may be the basis of clue (or it may be nonsense).

'when' is the link.

Can you help me to learn more?