Send over drink, accepting it's delayed the exercise (7)
I believe the answer is:
pilates
'the exercise' is the definition.
(pilates is a type of exercise)
'send over drink accepting it's delayed' is the wordplay.
'send over' is a reversal indicator (I've seen 'sent over' mean this).
'drink' becomes 'sip' (sipping is a kind of drinking).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'it's delayed' becomes 'late' (running late).
'sip' back-to-front is 'pis'.
'pis' placed around 'late' is 'PILATES'.
(Other definitions for pilates that I've seen before include "Ali's pet (anag) - exercise regime" , "discipline?" , "Pleats I arrange into a form of exercise" , "Set of exercises used in holistic medicine" , "Exercise system" .)