Record set by old church for long period (5)
I believe the answer is:
epoch
'long period' is the definition.
(I've seen this before)
'record set by old church' is the wordplay.
'record' becomes 'ep'.
'set by' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'church' becomes 'ch' (common abbreviation).
'ep'+'o'+'ch'='EPOCH'
'for' acts as a link.
(Other definitions for epoch that I've seen before include "Unit of geological time" , "remarkable time" , "Significant period" , "Division of a geological period" , "Distinctive period of time" .)