Clue: Reportedly bestow the title of 'sir' on Picaroon? Time to party till dawn! (4,1,5,2,2)
Answer: MAKE A NIGHT OF IT
Explanation: Definition: party till dawn!
This parsing requires a little care: sounds like ('reportedly') MAKE A KNIGHT OF ('bestow the title of 'sir' on') plus I ('Picaroon'; of course, the nominative does not match the previous expression, so must not be seen as part of it) plus T ('time')