After doing a little statistical analysis, time of the post appears have little effect in ranking until after the 48 hour mark of the competition. Then in compounds for every day later. The data set is limited but...
The top 3-5 tend to score significantly higher than other posts submitted before or between those posts often double or triple the point totals of the next highest ranked post. Posts from the first 24 hours are can easily drift down to the bottom quintile. Posts from the first 72 hours of the competition are over represented in the top quintile and under represented in the bottom; posts from the last 72 hours do not hold the same pattern in reverse. Both are generally well represented in all three middle quintiles.
Roughly half of all submissions are made in the first 24 hours, and 70-80% are made in the first 72.
Basically, an image posted in the first few hours is about as likely to end up in the fourth quintile as the second.
I can't say with any conclusiveness, but I suspect the remaining discrepancy may be down to the preparedness of the first few submissions. In order to submit in the first hour or two, you'd almost have to be following the competition closely enough to know what the next theme is going to be, which gives you an advantage just because you have more time to consider your submission.
As a personal example, I've been doing a lot of street photography since I moved to the NYC area 5 years ago. Since I saw that street photography was an upcoming category, somewhere in the back of my mind a part of me has been internally debating which image(s) from the hundreds in my catalog I might submit*. To my mind, that gives a competitor a distinct advantage over someone who discovered the contest theme when the contest was posted.
So as to a recommendation, this should reduce the impact and not drastically increase the work for Scott:
- Display the upcoming theme under the featured image about a week before it opens, "Upcoming Contest - Theme - Starts YYYY-MM-DD".
- Those interested in participating can check into the site any time after it is announced, giving them time to consider and warning them when the contest will open so they can get their submission in early.
- State the known issue in the rules and actively encourage competitors to submit their images on the first day of the contest if possible.
*And which I don't mind falling under the Creative Commons license, which is a far bigger consideration for me