Not on time, Greek character in cab, I suspect, beginning to hurry (1,3,4)
I believe the answer is:
a bit much
'not on' is the definition.
(both can mean unacceptable or unfair)
'time greek character in cab i suspect beginning to hurry' is the wordplay.
'time' becomes 't' (abbreviation).
'greek character' becomes 'mu' (letter from the Greek alphabet).
'in' means one lot of letters goes inside another.
'suspect' indicates an anagram (a suspicious or unusual spelling).
'beginning to' suggests taking the first letters.
The initial letter of 'hurry' is 'h'.
't'+'mu'='tmu'
'cab'+'i'='cabi'
'cabi' anagrammed gives 'abic'.
'tmu' placed inside 'abic' is 'abitmuc'.
'abitmuc'+'h'='A BIT MUCH'
(Other definitions for a bit much that I've seen before include "Too much to put up with, unreasonable" , "Somewhat unreasonable or OTT" , "unfair" , "over the top" , "unacceptable" .)