Play guitar having a time in bed (7)
I believe the answer is:
stratum
'bed' is the definition.
(thesaurus)
'play guitar having a time' is the wordplay.
'play guitar' becomes 'strum' (I've seen this before).
'having' is an insertion indicator.
'time' becomes 't'.
'a'+'t'='at'
'strum' enclosing 'at' is 'STRATUM'.
'in' acts as a link.
(Other definitions for stratum that I've seen before include "Social class - level" , "Bed of sedimentary rock" , "stretch of rock" , "rock band" , "(Geological) layer" .)