I know many will say the time ended, we must have bought before 15 days but I think this is the best time. Before couple of weeks ago, BTC was around $4k and which is why altcoins are overpriced in term of BTC. Now that BTC has gained price, altcoins price has decreased in term of BTC and now is the best time to pick your favorite altcoin because right after the BTC ride, altcoin will also follow the trend.
this is indeed the right time to buy an altcoin, but you have to choose the right altcoin before deciding to buy because not all altcoins will experience price increases when bitcoin rises, you have to choose potential altcoins that enter the top 20 CMC, because the coins are definitely will follow bitcoin prices when bitcoin rises