Most genuine from the time of leading others (9)
I believe the answer is:
sincerest
'most genuine' is the definition.
(I've seen this before)
'from the time of leading others' is the wordplay.
'from the time of' becomes 'since'.
'leading' means one lot of letters go next to another.
'others' becomes 'rest' (I've seen this before).
'since'+'rest'='SINCEREST'
(Other definitions for sincerest that I've seen before include "Most genuine" , "Least devious" , "Most dinky-di" , "least affected" .)