When importing a watch-only address over `importmulti` with a specific timestamp, the wallet's `nTimeFirstKey` will be set to 1.
I think we should add a optional timestamp to `CWallet::AddWatchOnly()` and use it when importing addresses or pubkeys.

{
    try {
        bool success = false;
        
        const UniValue& scriptPubKey = data["scriptPubKey"];
        
        if (!(scriptPubKey.getType() == UniValue::VOBJ && scriptPubKey.exists("address")) && !(scriptPubKey.getType() == UniValue::VSTR)) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid scriptPubKey");
        }
        
        const string& strRedeemScript = data.exists("redeemscript") ? data["redeemscript"].get_str() : "";
        const UniValue& pubKeys = data.exists("pubkeys") ? data["pubkeys"].get_array() : UniValue();
        const UniValue& keys = data.exists("keys") ? data["keys"].get_array() : UniValue();
        const bool& internal = data.exists("internal") ? data["internal"].get_bool() : false;
        const bool& watchOnly = data.exists("watchonly") ? data["watchonly"].get_bool() : false;
        const string& label = data.exists("label") && !internal ? data["label"].get_str() : "";
        bool isScript = scriptPubKey.getType() == UniValue::VSTR;
        bool isP2SH = strRedeemScript.length() > 0;
        const string& output = isScript ? scriptPubKey.get_str() : scriptPubKey["address"].get_str();
        
        CScript script;
        CBitcoinAddress address;
        if (!isScript) {
            address = CBitcoinAddress(output);
            script = GetScriptForDestination(address.Get());
        } else {
            if (!IsHex(output)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid scriptPubKey");
            }
            std::vector<unsigned char> vData(ParseHex(output));