For the Oracle version there are checks to make sure that the current valuation is above the amount loaned. There should be a similar check that the loan duration is not zero. Zero is not useful for flash loans because of the origination fees.
https://github.com/code-423n4/2022-04-abranft/blob/5cd4edc3298c05748e952f8a8c93e42f930a78c2/contracts/NFTPair.sol#L224
https://github.com/code-423n4/2022-04-abranft/blob/5cd4edc3298c05748e952f8a8c93e42f930a78c2/contracts/NFTPairWithOracle.sol#L244
