now buy with dolar euro gbp or some other currency and then sell after halving to gain some profit
Exactly. I think that the right time is especially now since Bitcoin's price has been heading downwards during the last days. It may be best to buy at these cheap prices to earn huge profits in the long run. Once price recovers between the $720 - $750 it should be enough to make good income. That is why Bitcoin may be the best investment due to its volatility which makes it very profitable.
A good strategy would be the following:
1. Buy low
2. Sell high
3. Exchange BTC to fiat pegged cryptos (like Tether, bitUSD etc) to preserve profits.
Just my opinion.