Depend on altcoin that you choose, indeed almost altcoin price will move depend on bitcoin price movement but there are some altcoin which have its own movement. As an example sushi coin, yesterday when bitcoin price decrease but not with sushi. This coin was increasing for almost 27% and until now it still increase.

The bull run market have made almost altcoin increase for more than 100%, look XRP and XLM price movement before the bull run came. So, I don't think this is a good time to buy altcoin especially if you choose for long term investment, but if you choose for short term investment or for trading purpose it's never too late to start you still have a high chance to gain profit.