Very sound advice. My take on BTC and alts is 3-fold. 1. BTC goes up a lot and alts go down (everyone rushing to BTC) 2. BTC is steady or goes up a bit, alts often go up a lot more (people are feeling confident in crypto and looking for value). 3. BTC goes down and alts go down more (flight to safety).
So the best time to invest in alts is when BTC is steady or rising gradually. We seem to be in a phase now like #1 where people are rushing back into BTC due to optimism over SegWit / scalability / conflict resolved.