Crossword Genius

It'll go up after a while (4,4)

Ross

I believe the answer is:

time bomb

I'm a little stuck... Click here to teach me more about this clue!

'it'll' is the definition.
I can't judge whether this definition defines the answer.

'up after a while' is the wordplay.
'up' becomes 'bomb' (I can't justify this - if you can you should give a lot more credence to this answer).
'after' means one lot of letters go next to another.
'a while' becomes 'time' (I've seen this before).
'bomb' after 'time' is 'TIME-BOMB'.

'go' is the link.

Can you help me to learn more?

(Other definitions for time bomb that I've seen before include "Exploding ticker?" , "one could go off after a while" , "Thing set to explode" , "Device set to explode later" , "Preset explosive device" .)

I've seen this clue in the Evening Standard.
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