Tours of duty (7)
(Other definitions for hitches that I've seen before include "Temporary problems or stoppages" , "Snags, temporary stoppages" .)
'tours of duty' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stints that I've seen before include "Stretches" , "Spells" , "Allots sparingly" , "Unbroken periods of work" , "Allotted work periods" .)