Submitted by ktg, also found by MiloTruck, KingNFT, and 0xTheC0der
According to the document (https://forum.arbitrum.foundation/t/proposal-security-council-elections-proposed-implementation-spec/15425/1#h-1-nominee-selection-7-days-10), security council election can be created every 6 months. Contract SecurityCouncilNomineeElectionGovernor implements this by these codes:
If electionIndex = 1, function createElection will call electionToTimestamp to calculate for timestamp 6 months from firstNominationStartDate. However, the code uses firstNominationStartDate.day to form the result day:
This could result in wrong calculation because the day in months can varies from 28-31. Therefore, the worst case is that the user has to wait for 6 months + 4 more days to create new election.
For example, if firstNominationStartDate = 2024-08-31-01:00:00 (which is the last day of August). The user might expect that they can create election again 6 months from that, which mean 1:00 AM of the last day of February 2025 (which is 2025-02-28-01:00:00), but in fact the  result of electionToTimestamp would be 2025-03-03-01:00:00, 4 days from that.
Below is POC for the above example, for easy of testing, place this test case in file test/security-council-mgmt/governors/SecurityCouncilNomineeElectionGovernor.t.sol under contract SecurityCouncilNomineeElectionGovernorTest and run it using command:
forge test --match-path test/security-council-mgmt/governors/SecurityCouncilNomineeElectionGovernor.t.sol --match-test testDateTime -vvvv
You can use an online tool like https://www.epochconverter.com/ to check that 1740963600 is Monday, March 3, 2025 1:00:00 AM GMT.
I recommend fixing the math so that the duration between elections are exactly 6 months like documented.
Math
yahgwai (Arbitrum) confirmed and commented:
