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.
for (CWallet::TxItems::const_reverse_iterator it = txOrdered.rbegin(); it != txOrdered.rend(); ++it)
    {
        CWalletTx *const pwtx = (*it).second.first;
        if (pwtx != nullptr)
            ListTransactions(pwallet, *pwtx, strAccount, 0, true, ret, filter);
        CAccountingEntry *const pacentry = (*it).second.second;
        if (pacentry != nullptr)
            AcentryToJSON(*pacentry, strAccount, ret);
        if ((int)ret.size() >= (nCount+nFrom)) break;
    }
    
    if (nFrom > (int)ret.size())
        nFrom = ret.size();
    if ((nFrom + nCount) > (int)ret.size())
        nCount = ret.size() - nFrom;
    std::vector<UniValue> arrTmp = ret.getValues();
    std::vector<UniValue>::iterator first = arrTmp.begin();
    std::advance(first, nFrom);
    std::vector<UniValue>::iterator last = arrTmp.begin();
    std::advance(last, nFrom+nCount);
    if (last != arrTmp.end()) arrTmp.erase(last, arrTmp.end());
    if (first != arrTmp.begin()) arrTmp.erase(arrTmp.begin(), first);
    std::reverse(arrTmp.begin(), arrTmp.end()); 
    ret.clear();
    ret.setArray();
    ret.push_backV(arrTmp);
    return ret;
}
UniValue listaccounts(const JSONRPCRequest& request)