Impertinence shown by terrible old ruler — time to run around (9)
I believe the answer is:
gallivant
'run around' is the definition.
(thesaurus)
'impertinence shown by terrible old ruler time' is the wordplay.
'impertinence' becomes 'gall' ('gall' can be a synonym of 'impertinence').
'shown by' means one lot of letters go next to another.
'terrible old ruler' becomes 'ivan' (Russian tsar Ivan the Terrible).
'time' becomes 't'.
'gall'+'ivan'+'t'='GALLIVANT'
'to' acts as a link.
(Other definitions for gallivant that I've seen before include "play around" , "run around" , "Pleasure-seek" , "Wander aimlessly" , "Go out seeking amusement" .)