When we have to sell Bitcoin and buy Altcoin?
Forking makes your Bitcoin higher,
so I can sell it.
These extra money can be used to buy (cheap) altcoins,... anyone has suggestion when do I have to start to buy it?
It actually going to be on the basis of where you have your allegiance. While some people will hold the believe that this is the time to buy altcoin, others will prefer to stick and hold their coins. In my own case, I would prefer to not sell all bitcoin for the sake of alt coin rather, I would spread my risk to ensure that I don't lose out on both ends and at the same time be more careful about the choice of investments in alt coins because as they could return profit quickly, they could also return losses as well.