What is Bitcoin Halving?
A specific number of Bitcoins is generated each time a new block is mined. Halving is the process that enables Bitcoin to control its supply and by which this number is cut in half. This halving is scheduled in height (The block height of a particular block is defined as the number of blocks preceding it in the blockchain) and not in date. A halving occurs every 210,000 blocks. Once the block subsidy expires, miners will be paid for securing the network by transaction fees.

(Source : https://www.investopedia.com/terms/b/bitcoin-mining.asp)
First Halving: November 28, 2012 at 15:24:38 (GMT)
Second Halving: July 9, 2016
Third Halving: May 13, 2020 (Estimated date)

Time to buy 1 Bitcoin for those who can

(Source : https://timeto.trade/en)
As can be easily seen, Bitcoin enters a vertical rally after each halving so it seems time for those who can afford it to buy Bitcoins before the third halving.
Some Stats:
- Total Bitcoins in circulation: 18 314 638
- Percentage of total Bitcoins mined: 87,21%
- Bitcoins generated per day: 1800
- more statistics can be found on https://www.bitcoinblockhalf.com/