If this is in regards to your planned trip with a pre-teen also on a bike, I think that the self discipline of the pre-teen is the most critical factor. I have seen adults swing out into traffic because they did not think there was any, fortunately I only observed strenuous braking and horn honking in those situations. Could have been much worse.
I think visibility is much more important than time of day. I know you asked for data, I have none. But I have the experience of close calls, so chose to elaborate anyway.
On this forum every time the question of theft prevention comes up, situational awareness is a major topic. I think the same thing here. If you are having trouble seeing ahead, the car driver behind you is too. If rainy or high humidity, you might also have to worry about the cars behind you not having good wipers or defrosters. The drivers in cars in front of you are a hazard too, but at least you can see them and try to assess as you approach.
I used to drive a vintage motorcycle to work every day. It was built before the law requiring motorcycle lights on full time, thus I had a light switch unlike the newer ones. And it did not have a very strong alternator, while city driving with low RPMs on the motor with headlight on my battery would steadily be discharging. Thus, sometimes I drove with my light off (was only pulled over once, no ticket). Over the decades of driving that in rush hour I concluded that on sunny days, even if I had my headlight off I was a lot safer than I was on overcast days with my headlight on or my high beam on. People can see so much more clearly on sunny days, but you don't realize that until all of your close calls occur on rainy days or overcast days. And after years of that you start to develop a sense for when the traffic is likely to see you, or not. In my case, I developed the rule of thumb that if I could not see shadows, I was invisible to traffic and I better behave that way. In other words - situational awareness.
I did my first ACA trip in 2012, a dozen riders. On day one, I was the only one that used my flashing taillight in daytime. After a week and some people noticed my taillight, by the end of the trip two others were using their flasher. Most did not have flashers at all, this was a decade ago and few were using them at that time.
All of my comments below refer to the photos under the comment.
ACA issues you these triangles when you go on one of their trips. I have started to use my triangle on my non-ACA trips too. I tried something below, instead of putting the triangle centered on my bike, I put it on the far left. It might have been my imagination, but I think the car drivers gave me a little more room when they passed me when the triangle was further to the left. Another advantage to it being on the left is that it is lower. And if the car behind you has headlights on, that reflective material might show up much better if the triangle is lower, but that depends on their lighting system and if their daytime lights are angled higher than nighttime low beams. I was surprised how much more noticeable that triangle was than my flashers on an overcast or rainy day when I was looking at my bike from behind.
On a pure safety issue, you can't beat wide shoulders.
This was very early morning leaving Everglades National Park in fog. There was amost no traffic, the few cars that did drive past us were driving slow too. You can see the outline of my travel partner in front of me in the fog as we rode towards the sunrise that would blind any drivers behind us. You can't see the shoulder in the photo, but there was very little shoulder.
I pulled over to the side of the road in the photo below to wait for the fog to lift, as I was too afraid of cars not seeing me. But after waiting for a while and seeing how slow the cars were that were driving past, I decided that with my two flashers on back, I would be reasonably safe because the cars were not much faster than I would be.
This was a lot less safe than it looks, weather was good, but traffic from behind was in and out of shadows, so for them it was intermittent bright sunlight in their eyes and intermittent dark. And the road was curvy and up and down so the cars could be on top of you with very little warning. And the brush growing into the road, some of that was thorn bushes so you did not want to ride too close, so you were far into the traffic lane.
On the day below, I decided that the bike trail was much slower and much muddier than taking a highway, but decided that the mud was probably safer as the road alternative was likely busy.
One thing on this forum that should be discussed more is sound. Do not risk relying on sound to know if a car is behind you. Hybrids and electric vehicles can be nearly silent. And there are more and more of those out there. Ask anyone that has worked on a road construction project where cars driving past only feet away if they can hear the hybrids or electric vehicles very well. Rear view mirrors are more important every year for us. I prefer helmet mount, a friend of mine prefers eyeglasses mount. I know a guy that likes it on his bar end, but he almost never looked in it because he had to tilt his head down to do so, so not sure why he had it at all.
Speaking of mirrors, on this bridge there was a lot of debris on the shoulder, even some 2X4 lumber. A few times I had to ride in the traffic lane due to the debris, I was glad to have a rear view mirror on my helmet. Otherwise I would have had to stop to get a good look behind me.
If I think of any more key topics, I will add it.