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.

}
    if (GetBoolArg("-upgradewallet", fFirstRun))
    {
        int nMaxVersion = GetArg("-upgradewallet", 0);
        if (nMaxVersion == 0) 
        {
            LogPrintf("Performing wallet upgrade to %i\n", FEATURE_LATEST);
            nMaxVersion = CLIENT_VERSION;
            walletInstance->SetMinVersion(FEATURE_LATEST); 
        }
        else
            LogPrintf("Allowing wallet upgrade up to %i\n", nMaxVersion);
        if (nMaxVersion < walletInstance->GetVersion())
        {
            InitError(_("Cannot downgrade wallet"));
            return NULL;
        }
        walletInstance->SetMaxVersion(nMaxVersion);
    }
    if (fFirstRun)
    {
        
        if (GetBoolArg("-usehd", DEFAULT_USE_HD_WALLET) && !walletInstance->IsHDEnabled()) {
            
            CPubKey masterPubKey = walletInstance->GenerateNewHDMasterKey();
            if (!walletInstance->SetHDMasterKey(masterPubKey))
                throw std::runtime_error(std::string(__func__) + ": Storing master key failed");
        }
        CPubKey newDefaultKey;
        if (walletInstance->GetKeyFromPool(newDefaultKey)) {