Attach too much importance to the speed of deliveries? (8)
I believe the answer is:
overrate
'attach too much importance to' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
(Other definitions for overrate that I've seen before include "Rank too highly" , "Value or assess too highly" , "Exaggerate" , "Inflate" , "Make too high an estimate of" .)