The first two runs ended exactly one year after the mining reward halving.
E.g. December 2016 => Dec. 2017
IMO it will be the same this time, May 2020 => May 2021
So we shall assume the price the BTC will have in May will be the maximum for this cycle?
Should we sell in May?
This is not the right approach to estimate the end of bull market and sell on whatever the price is in May. No one knows exactly how when this bull market will end. Currently the bitcoin price is only 2x from its all time high and therefore as per the previous history we are no where near the peak of this bull run.
Bull market may end few months before or after december 2021 but only time will tell.