Well since its a market timing thread, I'll give my take. I agree with in your first five years of retirement you have to basically have at least a decent sized chunk of your portfolio in something safe, so you can absolutely ride out a recession without having to go back to work.
That said, I view the market from a statistical sense, in that bull markets generally tend to be quite a bit longer than bear markets. I also view the switch between a bull/bear from a probabilistic viewpoint. E.g., at the very beginning of a bull, the chance of a bear occurring basically starts out at 0%, and slowly edges up from there. However based on history, it is not until about 5-6 years into a bull before the chance of a bear happening reaches 50%, and of course it goes up from there. As such, I believe that before that 50% point is reached, if in the accumulating phase, it is ideal to have a higher risk allocation than your general ideal portfolio mix, and after that 50% point is reached, to be prepared to a lower risk allocation.
The other interesting thing is about bear's statistical 50% switch point, it seems to be only about 12 months after a bear begins, so it isn't all that smart to "stay out" for anywhere near the same period you need to be "staying in" and going long. You basically have a 6:1 chance of getting burned if you do it truly randomly, and obviously the odds are much worse if you have a very low risk tolerance, or better if you have a very high risk tolerance.
This is the timeline I setup for myself many years ago: 2009 heavy buy, 2010 heavy buy, 2011 heavy buy, 2012 light buy, 2013 light buy, 2014 neutral, 2015 light sell, 2016 light sell, 2017 heavy sell, 2018 heavy sell. Basically at 2014, around April, I will switch to my ideal mix, 70/30 from 100/0, in 2017 I will switch from 70/30 to 40/60, if a bear hasn't hit by April 2019, I may switch to 20/80. Once a bear hits, you can bet I will go 100/0 about 12-18 months into it, whenever I see a sustained 2-4 week upswing.
Just the way I've been investing for about a decade, and what I plan to do next decade as well. In retirement I will more quickly switch into and hold my ideal asset allocation than I would while accumulating. I likely would switch to 70/30 only 3-4 years into a bull.