Row when stopwatch loses minute (4)
I believe the answer is:
tier
'row' is the definition.
(a tier is a row of things)
'stopwatch loses minute' is the wordplay.
'stopwatch' becomes 'timer' (I've seen this in another clue).
'loses' indicates named letters should be taken away.
'minute' becomes 'm' (abbreviation).
'timer' with 'm' taken out is 'TIER'.
'when' is the link.
(Other definitions for tier that I've seen before include "Row - one forming a knot" , "Level within hierarchy" , "Bank - row" , "band" , "one doing Bond" .)