Period in which monarch managed to create order (7)
I believe the answer is:
arrange
'order' is the definition.
(I know that order can be written as arrange)
'period in which monarch managed' is the wordplay.
'period' becomes 'age' (age is a kind of period).
'in which' is an insertion indicator.
'monarch' becomes 'R' (abbreviation for rex, king in Latin).
'managed' becomes 'ran' (I've seen this before).
'r'+'ran'='rran'
'age' going around 'rran' is 'ARRANGE'.
'to create' is the link.
(Other definitions for arrange that I've seen before include "position" , "Set in place" , "Organise, plan" , "Settle, work out" , "Sort" .)