Former common feature of past, present and future? (3-4)

'former' is the definition.
(I know that former can be written as one-time)

'common feature of past present and future?' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
'future?' could be 'time' (future is a kind of time) and 'time' is found in the answer.
A single letter 'e' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?