Anytime is the good time to buy or invest on Altcoins and you need to do is to make some research about the Altcoin that you're going to buy and watch it in coinmarketcap.com and look for the history price chart. If it's dropping then you could buy now otherwise wait a little longer because Crypto Market is volatile and almost every Altcoin are dumping and pumping every other day so wait for a good timing and hit Buy Button if the coin price is lower.