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.
+ HelpExampleCli("walletlock", "") +
            "\nAs a json rpc call\n"
            + HelpExampleRpc("encryptwallet", "\"my pass phrase\"")
        );
    }
    LOCK2(cs_main, pwallet->cs_wallet);
    if (request.fHelp)
        return true;
    if (pwallet->IsCrypted()) {
        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an encrypted wallet, but encryptwallet was called.");
    }
    
    
    SecureString strWalletPass;
    strWalletPass.reserve(100);
    strWalletPass = request.params[0].get_str().c_str();
    if (strWalletPass.length() < 1)
        throw std::runtime_error(
            "encryptwallet <passphrase>\n"
            "Encrypts the wallet with <passphrase>.");
    if (!pwallet->EncryptWallet(strWalletPass)) {
        throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, "Error: Failed to encrypt the wallet.");
    }
    
    
    
    StartShutdown();
    return "wallet encrypted; Bitcoin server stopping, restart to run with encrypted wallet. The keypool has been flushed and a new HD seed was generated (if you are using HD). You need to make a new backup.";
}
UniValue lockunspent(const JSONRPCRequest& request)