According to new analysis, presented Sept. 8, the amount of time it is necessary to have held Bitcoin to make a profit is 1,335 days or roughly 3 years and 8 months. This roughly correlates to the four-year cycle length based on reward halving periods.
While a 100% sure profit would have taken a maximum of 1,335 days, this relates to the bull-run in late 2013, when Bitcoin price surged to $1150. If you had bought in right at the top, then it took 1,335 days before Bitcoin finally broke that level in early 2017.