Two minutes to crack one exam? Wicked! (7)
I believe the answer is:
immoral
'wicked' is the definition.
(similar in meaning)
'two minutes to crack one exam?' is the wordplay.
'two minutes' means two substitutions for 'minutes'.
'minutes' becomes 'm' (common abbreviation).
'minutes' becomes 'm' (common abbreviation).
'to crack' means one lot of letters goes inside another (inserted letters go into a gap or crack).
'one' becomes 'i' (Roman numeral).
'exam?' becomes 'oral' (spoken academic test).
'm'+'m'='mm'
'i'+'oral'='ioral'
'mm' going inside 'ioral' is 'IMMORAL'.
(Other definitions for immoral that I've seen before include "sick" , "Promiscuous" , "Abandoned" , "Not conforming to accepted rules of conduct, particularly in sexual matters" , "Ethically unprincipled" .)