I was just following a thought I had yesterday. I only have a few months of data, but I notice how I usually see that a day is volatile or quiet right from the opening hour or so and I've heard others comment similarly. So I took a few months (if anyone knows how I can get hourly SPY data for free that's a longer sample I would appreciate it and will redo/repost the results). I was wondering how predicitve of the day the opening hourly range is of the range of the entire day. Here are my results.
Average multiplier of the hourly opening range was 2.93
The median multiplier of the hourly opening range was 2.33
The days range was almost never less than twice the range of the opening hour.