This graph shows the proportion of times and days of the week when users are active in the subreddit.
Note the increased activity during Tuesdays/Wednesdays (and earlier Sundays/Mondays), when new runs start and new members are added.
For reference, this is when midnight hits in some timezones (in GMT):
North American Central Time (CST) = 06:00
Brasilia Central Time = 3:00
European Central Time (CET) = 23:00
Arabian Standard Time = 21:00
China Standard Time (CST) = 16:00
Australian Central Standard Time (ACST) = 14:30