If I unlock an encrypted wallet for 359711509437336256 or less seconds, I can sign transactions with it:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336256
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
      "complete": true

But if I unlock it for 359711509437336257 or more seconds, it appears to have unlocked but I can't sign any transactions:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336257
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
    error code: -13
    error message:
    Error: Please enter the wallet passphrase with walletpassphrase first.

I don't know the significance of that number. It's nowhere near a power of 2.

I was trying to unlock the wallet effectively "forever", so put a big number. If I use too big a number (2^63 or more) I get an error message `JSON integer out of range` but for numbers between 359711509437336257 and 2^63-1 inclusive I get no error, but no actual unlocking.
"\nExamples:\n"
            + HelpExampleCli("listreceivedbyaccount", "")
            + HelpExampleCli("listreceivedbyaccount", "6 true")
            + HelpExampleRpc("listreceivedbyaccount", "6, true, true")
        );
    ObserveSafeMode();
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK2(cs_main, pwallet->cs_wallet);
    return ListReceived(pwallet, request.params, true);
}
static void MaybePushAddress(UniValue & entry, const CTxDestination &dest)
{
    if (IsValidDestination(dest)) {
        entry.push_back(Pair("address", EncodeDestination(dest)));
    }
}
/**
 * List transactions based on the given criteria.
 *
 * @param  pwallet    The wallet.
 * @param  wtx        The wallet transaction.
 * @param  strAccount The account, if any, or "*" for all.
 * @param  nMinDepth  The minimum confirmation depth.
 * @param  fLong      Whether to include the JSON version of the transaction.
 * @param  ret        The UniValue into which the result is stored.
 * @param  filter     The "is mine" filter bool.
 */
void ListTransactions(CWallet* const pwallet, const CWalletTx& wtx, const std::string& strAccount, int nMinDepth, bool fLong, UniValue& ret, const isminefilter& filter)