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.params[1].get_bool())
            filter = filter | ISMINE_WATCH_ONLY;
    UniValue entry(UniValue::VOBJ);
    auto it = pwallet->mapWallet.find(hash);
    if (it == pwallet->mapWallet.end()) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid or non-wallet transaction id");
    }
    const CWalletTx& wtx = it->second;
    CAmount nCredit = wtx.GetCredit(filter);
    CAmount nDebit = wtx.GetDebit(filter);
    CAmount nNet = nCredit - nDebit;
    CAmount nFee = (wtx.IsFromMe(filter) ? wtx.tx->GetValueOut() - nDebit : 0);
    entry.push_back(Pair("amount", ValueFromAmount(nNet - nFee)));
    if (wtx.IsFromMe(filter))
        entry.push_back(Pair("fee", ValueFromAmount(nFee)));
    WalletTxToJSON(wtx, entry);
    UniValue details(UniValue::VARR);
    ListTransactions(pwallet, wtx, "*", 0, false, details, filter);
    entry.push_back(Pair("details", details));
    std::string strHex = EncodeHexTx(*wtx.tx, RPCSerializationFlags());
    entry.push_back(Pair("hex", strHex));
    return entry;
}
UniValue abandontransaction(const JSONRPCRequest& request)
{
    CWallet * const pwallet = GetWalletForJSONRPCRequest(request);
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() != 1)