It depends on you, nothing more than that. I would just buy when i see a dip on the market, not on the top because the prices are always going lower than that, but it also depends on the moment and the current market conditions
I think the current time is very good to buy into altcoin and hold until the end of this year. I believe that at the end of the year when the market is booming, Bitcoin is attracting so much money from the altcoin that so many altcoin are so low that investors can take advantage of this opportunity.