A material that can be made - whenever (2,4)

I believe the answer is:

at will

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

'can be made whenever' is the definition.
I can't tell whether this defines the answer.

'a material' is the wordplay.
'material' becomes 'twill' (twill is a kind of material).
'a'+'twill'='AT WILL'

'that' is the link.

Can you help me to learn more?

(Other definitions for at will that I've seen before include "take it as I please" , "Whenever one pleases, say fire rifle" , "whenever you want" , "Whenever you please, as you like" , "Freely" .)

I've seen this clue in The Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.