Like other people have said, it is about time zones.
Thats why I think leagues should be divided up by start times.
Using GMT, you choose your league. Throw in a day of the week and you have yourself a good structure.
Something like this:
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Hello, welcome to the GT Planet League signup list. You can jump into the middle of a season if you like, just know that may handicap your ability to win or place high in that league.
Please choose a start time/day that you would like. Each designated start time/day is a league. You will be expected to be there to join into the race at the designated time and day, each week.
We run leagues based on a 6 week cycle. So, try to plan accordingly and be there at your league's time/day. However, we know, it is not always possible to be there at your league's time/day every week. Life happens and we all expect that to happen to all of us.

So, we allow for one "freebie". In other words, if you make it to 5 of the 6 weeks, then you will not be penalized. But we also want to reward those who are there every time, so we will give a small bonus to those who are.
So, without further adieu here are the possible leagues to choose from:
[Saturday Leagues]
League A- 12:00 GMT Saturday
League B- 16:00 GMT Saturday
League C- 20:00 GMT Saturday
League D- 24:00 GMT Saturday
League E- 04:00 GMT Saturday
League F- 08:00 GMT Saturday
[Sunday Leagues]
League ABCDEF/Times
[Weekday Leagues]
League ABCDEF/Times
Qualifying:
Qualifying is held for each league. The event will be posted 24 hours after your league's last event. i.e. If you are part of [League A- 12:00 GMT Saturday], expect next weeks event to be posted by 12:00 Sunday. Please set a qualifying lap during the week and turn it in 24 hours before your leagues start time. i.e. If you are part of [League A- 12:00 GMT Saturday], then you would need to turn in your qualifying lap by 12:00 GMT Friday.
Please understand that qualifying plays a huge role. Half the points that can be awarded during a "season" can be awarded for qualifying. With the other half coming from the races that take place during your league's start time. Also, at the end of each season, there will be separate awards given to those who continually qualified well during the season.
So, please feel free to qualify even if you know you cannot make the event that week.
And of course, qualifying will determine your grid position!
So, Good Luck Guys, And remember that the main objective is to have a great time.
______________________________________
Well, that's kind of how I see it. I hope you guys get some good ideas from it.
p.s. I would just scatter about 3 or 4 leagues throughout the week since weekend leagues will be much more popular. Such as this:
[Weekday Leagues]
League A- 08:00 Tuesday
League B- 12:00 Wednesday
etc...
Also, you can make it where each league has a partner league. So, if you qualify all week and can't make it to your start time on Saturday, then you can try and switch to your "Sister League". Which will be running the exact same event that week. Or what I would prefer, is that all GT Planet leagues run one event each week. Keeping it similar to the WRS. It would keep the logistics easier and would probably be more fun since all of GT Planet is posting times with the same combo.
But again, this is just "out loud brainstorming", so use what you want and throw the rest away. 👍