A graduate securing second degree ultimately is simple creature (6)
I believe the answer is:
Here is my best explanation:
'simple creature' is the definition.
(I've seen this before)
'a graduate securing second degree ultimately' is the wordplay.
'graduate' becomes 'ba'.
'securing' means one lot of letters goes inside another.
'second' becomes 'mo' (both are short periods of time).
'ultimately' indicates one should take the final letters.
The last letter of 'degree' is 'e'.
'aba' going around 'moe' is 'AMOEBA'.
'is' acts as a link.