Is that how many runs were under 46 seconds ? If so your graph appears to show heat 1 as having the most.
That graph shows times under 46 seconds. Heat 1 did have more times under 46, but on average for the top 60% of the fastest cars in each heat, heats 2 and 3 were significantly faster.
I'm not picking on novices here, but novices tend to run in heat 2 and most likely heat 3. That is why I believe you see heat 1 times eventually become faster than the other heats. That may also be why heat 2 was faster than 3. Or maybe the track got too warm and times got a little slower. Or maybe just the majority of the faster cars ran in heat 2.
This is just for fun and not meant to make an excuse for my sucky time.
Heat does have an effect on tires but different effects on street vs Race compounds a spray bottle of water can take care of that , but a novice in a later heat may not check his or her tire pressures between runs and start to slide more as the pressures raise. For weathered "a few years or more" autocrossers it may just depend on what the driver wants. If your "me" and you run heat 1 and work heat 2 you can go early and get your schoolwork that you have been procrastinating all week done... This may also be the case for people who have to travel for an hour or more to the event.. Or if you run heat 3 you can get your worker assignment done early and have the middle of the day to have a pizza delivered and watch where everyone messes up and take note : ) heat 2 runners have plenty of time to watch, eat and prep their cars so they all have advantages.