The most common and most likely answer to this crossword clue is the 6 letter word MAÑANA
I've seen this crossword clue in The Guardian
M
A
Ã
‘
A
N
A
More clues leading to the result MAÑANA
- Mum and gran are coming together tomorrow
- Mum meeting Granny? Any time will do
- Mother and grandmother provide a vague timeline
- Two relatives meeting tomorrow in Madrid?
- Answer may appear in godsend some day
- Eventually having good fortune to hold ace
- Two female relatives meeting tomorrow
- Food from heaven comes around afternoon tomorrow
- Chap with stories for some other time
Buddy explains!

The straight part
We know that "a vague timeline" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a vague timeline = maÑana.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MAÑANA mean?
MAÑANA adverb- Tomorrow.
- Sometime in the future. Usually to say in a satirical sense 'sometime in the unspecified future, despite the fact that we were told tomorrow without fail'.