Whale’s time with expert in the sea, nothing less (8)
I believe the answer is:
cetacean
'whale's' is the definition.
(I've seen this before)
'time with expert in the sea nothing less' is the wordplay.
I cannot really see how this works, but
'time' could be 't' (abbreviation) and 't' is found within the answer.
'expert' could be 'ace' (ace can informally mean very good) and 'ace' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cetacean that I've seen before include "Encase cat with mammals like whales and dolphins" , "Member of the animal order containing whales and dolphins" , "Large marine mammal" , "One swimming" , "Animal order including whales and dolphins" .)