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.
{
    if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            "listwallets\n"
            "Returns a list of currently loaded wallets.\n"
            "For full information on the wallet, use \"getwalletinfo\"\n"
            "\nResult:\n"
            "[                         (json array of strings)\n"
            "  \"walletname\"            (string) the wallet name\n"
            "   ...\n"
            "]\n"
            "\nExamples:\n"
            + HelpExampleCli("listwallets", "")
            + HelpExampleRpc("listwallets", "")
        );
    UniValue obj(UniValue::VARR);
    for (CWalletRef pwallet : vpwallets) {
        if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
            return NullUniValue;
        }
        LOCK(pwallet->cs_wallet);
        obj.push_back(pwallet->GetName());
    }
    return obj;
}
UniValue resendwallettransactions(const JSONRPCRequest& request)