Both BTC and ETH is good to invest right now you just need to study the crypto market before you invest on it. If you do not know how to invest properly then you will probably lose what you have invested. The BTC is good for long term investment, they have both good for investing now because the price in the market is becoming good already. There is no specific time how long you will hodl them because it will depend on the price in the market. The best time to buy coin is when the price is dump right now have to wait for the price to dump because as I have checked the prices in the is playing with $7k - $8k you should buy when the price is at $5k so that when you hodl it will make double.