If the bull market recur periodically, like what happened in late 2017, how long dose a cycle would take? It seems at least longer than a year now..
Bitcoin is still too young to find well enough a pattern.
From what
I see on the graphs (if you go to the link, set it to 3 days period) I think that the other significant bull run was the MtGox one, with about 1.5-2 years (2014, 2105) of bad and worse prices, then more than one year of slow recovery (2016 and part of 2017) to see a 8-9 months bubble (Apr-Dec 2017)
However, get the graphs and look for yourself...