Dear Codeforces.
Today, I wrote about a mystery of Codeforces contest start time.

1 — Background

There are many codeforces users from many countries. In spite of this, recently I feel Codeforces contest time is too biased and it's difficult to participate or enjoy for some country. For example, Codeforces Round #434 started at 13:05 UTC, Round #433 started at 12:55 UTC and Round #432 started at 14:35 UTC. It have only around 3 hours difference between "the earliest of the 3" and "the latest of the 3".
This is also an answer of "why I wrote this blog".

2 — Codeforces Time Distribution Graph

First, to investigate actual codeforces time, I searched recent 100 contests time and made a distribution graph.

3 — Problem

Recently, I found that Codeforces Contest times are biased and they're difficult to participate for some people:

• Around 9000 out of 30000 (30%) active users are difficult to participate because they're too late time. (China, Japan, South Korea, etc.)
• Around 3000 out of 30000 (10%) active users are difficult to participate because they're too early time. (United States, Brazil, Canada, etc.)

For example, the standard time in Beijing is UTC+8, so around 65% of contest starts at 22:00 or later, and ends at 24:00 or later. A large amount of participants are students, and I think 24:00-03:00 is too late time for student. If they saw systemtest and rating change, the sleeping time could be one hour later.

The other example is in New York. The standard time is UTC-5, so around 95% of contest starts at 12:00 or earlier, and ends at 14:00 or earlier. I think it is too early time, and the time overlaps for most people because of school or working. They can wake up more earlier, but I think morning is busy time for the most, so it's difficult to make time to participate a single contest in morning.

4 — My Suggestion

I think it is better that codeforces do this:

• ~20 or ~30 percent of contest should move in range 06:00-12:00 UTC. It's better time for Chinese, Korean, Japanese, etc. (It is also possible time for Indians, etc.)
• ~15 or ~20 percent of contest should move in range 21:00-03:00 UTC. It's better time for American, Canadian, Brazilian, etc.

This system in my suggestion is like TopCoder. (Contest time is not too biased)

I think this made some good effects and bad effects as follows:

• It became just a little bit more difficult to participate Codeforces contest for Indian, Russian, etc.
• It became more easier greatly to participate Codeforces contest for Chinese, American, etc.
• On the whole, I think active users would increase because it seems that there are many people who didn't cannot participate because of time.

This is just my suggestion, but I think this is also a strategy to increase users and to make codeforces more active.

Thank you for listening.