Its based on how fast you solve the puzzle after it is released at midnight EST. Each puzzle has two parts so each one gets a different placement. This site doesn't require you to actually upload the code, rather it gives you your own input file and you just need to submit the answer.

Day 2 recording is up. Placed 126th for part 1 and 245th for part 2. There were server issues on the site as well which slowed things down a bit.

youtu.be/fq51AcZusSk?...