Measure of length of payment time (4)
I believe the answer is:
feet
'measure of length' is the definition.
(foot is a unit of length)
'payment time' is the wordplay.
'payment' becomes 'fee' (I've seen this before).
'time' becomes 't' (abbreviation).
'fee'+'t'='FEET'
'of' is the link.
(Other definitions for feet that I've seen before include "Three of these in yard" , "Have both on the ground to be practical" , "Old measures - that fill shoes" , "Lower extremities" , "Measures - body parts" .)