Exercise time before shower (5)
I believe the answer is:
train
'exercise' is the definition.
(I know that train is a more specific form of the action exercise)
'time before shower' is the wordplay.
'time' becomes 't' (abbreviation).
'before' says to put letters next to each other.
'shower' becomes 'rain' (rainfall).
't'+'rain'='TRAIN'
(Other definitions for train that I've seen before include "Coach - string of coaches" , "Rail transport" , "Choo-choo or part of wedding dress" , "Linked carriages" , "one thing after another" .)