I dont think someone can pinpoint the right moment to invest in alternative coins. The market is very volatile and unpredictable.
The market of bitcoin as well altcoins will be completely volatile throughout. Very few stable coins were into usage on trading needs. Before buying altcoins go through the growth chart as well the increased chance of growth and possibilities to sell it on time. In this way it is good to buy low priced top listed altcoins to get a bigger earning at the shortest.