Hello, namnam. Welcome to this forum.
The forex market does not actually open or close during the week. But, forex trading volume is heavy during the normal business hours in each country, and much lighter during the rest of the 24-hour day.
So, it is convenient to use the normal business hours in each country as the forex session time for that country.
8am-5pm is a sort of average time period for the normal business day. But, local customs tend to differ in some countries. So, the best we can say is that forex trading volume in each country roughly conforms to this average 8am-5pm business day.
My studies of forex trading volume indicate that about 83% of each day’s volume occurs during the 9 hours between 8am and 5pm each day. And about 17% of each day’s volume occurs during the remaining 15 hours of the day. So, even though this 8am-5pm period is an approximation, nevertheless, it works pretty well.
You did a great job converting those times. Your table of session times is perfect. And the conclusions you have drawn regarding session overlaps are accurate, as well.
I was going to refer you to the Babypips School, where all these times were worked out long ago. But, as I was preparing to post a link to the page in the School where there is a table similar to yours, I found that someone has altered some of the times in that table, and it is no longer usable.
I have taken a screen-shot of the Babypips table which contains these errors, and I will post it in the “Bugs and Suggestions” forum. I hope that the Babypips people will act quickly to correct their table.
In the meantime, you may rely on the table you have constructed.
I should point out one thing, however. In the spring, when many countries begin switching from standard time to daylight saving time, there will be a period of several weeks when your table will be wrong, because those countries do not make the change to daylight saving time on the same date.
And then in the fall, when those countries switch back to standard time, the same thing happens again, because they don’t make the switch on the same date. These transition periods cause a lot of confusion for forex traders.
Here is a resource that you might want to study — 301 Moved Permanently
p.s. — Here’s my post in the “Bugs and Suggestions” forum — 301 Moved Permanently