The most common and most likely answer to this crossword clue is the 7 letter word AIRTIME
I've seen this crossword clue in The Daily Telegraph
A
I
R
T
I
M
E
Buddy explains!
The straight part
We know that "how long programme goes on for" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case how long programme goes on for = airtime.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 AIRTIME mean?
AIRTIME noun- The duration during which a radio or television program (or part of one) is transmitted.
- The chargeable use of a mobile phone, either in minutes or in units dependent on the use or traffic.
- The period during which a person riding a rollercoaster or similar ride experiences a feeling of weightlessness.