Technical reference
ERC-2612: a permit deadline is not an allowance expiry
The time limit governs submission of the signature, not necessarily the life of the resulting approval.
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What a permit changes
ERC-2612 lets an owner sign an approval containing a spender, value, nonce and deadline. A valid submitted permit updates the owner's allowance and advances the nonce. The owner need not submit the onchain transaction personally; another party can relay the signature.
Two different clocks
The deadline limits when the permit may be accepted. Once accepted, the resulting ERC-20 allowance does not automatically disappear when that deadline passes. For example, a permit accepted just before noon can leave spending authority after noon. Treating the signing deadline as the approval's expiry misstates the exposure.
After an unexpected signature
Identify the token contract and spender, determine whether the permit has been submitted, and inspect the resulting allowance. A revoked allowance and an unused signed permit are different states. An unexpired authorisation that still has the expected nonce may remain submit-able. A response must account for both the current approval and outstanding signatures.