From a very long perspective the best times to buy massive amounts of BTC for the long haul has been at the 4 year (1460 Day MA). When price falls below this area it has so far been a tremendous discount for the long term. I do want to caution however that when this happens, there can be wild swings and an increase in volatility in the near term. We could easily wick down to 14k in a quick panic and not think twice about it.
From a trend trading perspective we are still fairly far from what I would consider bullish. And I'm talking near 36k with staying power. I'm not saying that BTC won't only go up from here, I'm just saying that from a risk management perspective there's no way to honestly tell where we're headed near term.