I think there is no specific time to invest in Bitcoin,

However, As you begin to notice the time of day most activity occurs, you will be able to determine weekly patterns, i.e., the days that most trading activity occurs. Usually, prices drop when the market is less busy as trading volumes are lower. While cryptos are traded 24/7, activity generally decreases on weekends when all major stock markets are closed. Hence, the better times of the week to trade are likely when stock markets are active.

Also, some events affect the market,  such as the BTC Halving, which takes place every four years – have also historically been proven to impact cryptocurrency pricing trends.

But yes I would suggest to use crypto news apps like Cryptoreach that will accurately tells you the price and monthly returns of the bitcoin. So that you can follow your own strategy of investing in bitcoin.