No longer having time, stop -- or run on? (6)
I believe the answer is:
Here is my best explanation:
'run on?' is the definition.
'no longer having time stop' is the subsidiary indication.
'no longer' becomes 'ex'.
'having' is a charade indicator (letters next to each other).
'time' becomes 't'.
'stop' becomes 'end' ('end' can be a synonym of 'stop').
'or' is the link.
(Other definitions for extend that I've seen before include "Stretch, reach", "Stretch out, say the hand of friendship", "Lengthen", "Enlarge, widen", "Spread - offer", "Reach out or stretch", "Stretch out - enlarge", "Hold out or stretch out", "Stretch out over a distance or lengthen in time" and "Draw out".)