I don't think it's wise to judge based on the peaks and bottoms. Those are the outliers. The price touched there for a fleeting moment and then backed away. I'd rather calculate a trend-line over a long timespan that covers multiple boom-bust cycles, and note when the price crosses it. When the price is below the line, that's a relatively better time to be buying, if you have spare cash, and when it's above the line, that's a relatively better time to be selling, if you have the stocks.
You'll drive yourself crazy trying to predict the optimal timing for large orders.
Putting in a little at a time, or taking out a little at a time, based on broad criteria and your own goals as an investor, is way better than intensive analysis or day-trading. Once a paycheck or once a month is fine. Even better if you can set it up to be automatic, and you don't have to think about it too much.
Unfortunately, I don't have any spare cash, but those who heeded the warning of inverted yield and switched from "gradually buy" to "gradually sell" back then probably have enough cash savings and downward movement to switch back, or to at least stop selling for a while.