That's entirely different from trying to time the market upturns and downturns. If you need less risk and more liquidity then you should adjust your stocks/bonds asset allocation to match your risk tolerance and life goals, but within each bucket you should buy low-cost diversified index funds and hold them.
Only barely (see "What if we could perfectly time the market?" in [0] which cites [1]), and it is the height of self-delusion for anyone to think he or she will time it correctly, when professionals fail to do so. Don't try!
No it isn't! It's better to buy and hold and ride it out. Otherwise you tend to miss the gains on the other side. Decades of research by now has shown that buy-and-hold beats timing the market every time.