31 CFR 103.100 states, "Upon receiving an information request from FinCEN under this section, a financial institution shall expeditiously search its records..."

If a bank searches its records more than 14 days after receipt of an information request and does not have any positive matches, is it a violation of law?

Technically. As you quoted, you are supposed to search it as soon as possible. I'd be more concerned why this took so long to complete and change the procedures.

I agree with David.

"is it a violation of law? "

The regulators think so.

So what would be an acceptable time frame for this search to take place?

FinCEN time requirements for reporting back to them is 14 days. Anything over that is going cause grief with the regulators. While you might try the argument that there were no matches so there is no violation - I just don't think it will hold much water with the examiners from what I have experienced. They will site:

103.100(b)(2) (ii) Report to FinCEN. If a financial institution identifies an account or transaction identified with any individual, entity, or organization named in a request from FinCEN, it shall report to FinCEN, in the manner and in the time frame specified in FinCEN's request, the following information:......

Our OCC examiner recommended that our searches be completed within 10 days then there would be sufficient time to notify FinCen before the 14 days are up. We get the searches on Tuesday and we try to have them back and validated on the FinCen website by Friday. And no, we've never had a match.

While you may have 14 days to RESPOND, you do not have 14 days to begin your search - assuming your regulator is going to take a FinCEN FAQ as gospel.

From FinCEN's 314(a) FAQ:

3. How quickly must a financial institution respond to a 314(a) request?
Financial institutions must begin searching their records immediately upon receiving a 314(a) request. If an institution receives a 314(a) request during non-business hours or during the weekend, it must commence its search the next business day. If a financial institution finds a match with a named subject, the match must be reported to FinCEN. Unless the instructions to a request state otherwise, financial institutions must complete their search on all the subjects listed in the 314(a) request and respond with any matches no later than fourteen (14) calendar days after receiving a 314(a) request.[emphasis added]