I think, it doesn't matter if we buy crypto when bitcoin prices have a high price because to be able to get profit not only in bitcoin but we also have to be able to find opportunities in each crypto currency so we will have many opportunities to get profit
Yes, I think the best time to buy is when altcoins are down and bitcoin is up because we can be able to have more capital buying cheaper altcoins. In that way we can be able to achieve high profit.