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("getnewaddress", "")
            + HelpExampleRpc("getnewaddress", "")
        );
    LOCK2(cs_main, pwallet->cs_wallet);
    
    std::string strAccount;
    if (!request.params[0].isNull())
        strAccount = AccountFromValue(request.params[0]);
    if (!pwallet->IsLocked()) {
        pwallet->TopUpKeyPool();
    }
    
    CPubKey newKey;
    if (!pwallet->GetKeyFromPool(newKey)) {
        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, "Error: Keypool ran out, please call keypoolrefill first");
    }
    CKeyID keyID = newKey.GetID();
    pwallet->SetAddressBook(keyID, strAccount, "receive");
    return EncodeDestination(keyID);
}
CTxDestination GetAccountAddress(CWallet* const pwallet, std::string strAccount, bool bForceNew=false)
{
    CPubKey pubKey;
    if (!pwallet->GetAccountPubkey(pubKey, strAccount, bForceNew)) {
        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, "Error: Keypool ran out, please call keypoolrefill first");
    }
    return pubKey.GetID();
}
UniValue getaccountaddress(const JSONRPCRequest& request)