I actually feel that this is more of a restriction of members because from what I understand is that for example, and I don't mean this rudely, that while you playing the game with a friend, an that's probobly the only time that day you can get on on the certain day. And all of a sudden you just get logged out of the game and can't get back on. I'd find that to be inconvenient for I know people will end up not liking this and make multiple accounts, if my idea is correct. If I'm wrong please correct.
It isn't a restriction on playing times in game, it's only a restriction on signing up as a new member.
Just adding to here since you mentioned,
"And all of a sudden you just get logged out of the game and can't get back on." The only place an individual should be having that problem in is in Fluorite. Fluorite Plains is the only map that during some parts of the day gets crowded and most everyone who isn't already on the map can't get in because it's at full capacity. If you find yourself with a character of yours stuck on that map or any map for that matter all you have to do is use the forum character reset option. There is no need to make multiple accounts. It's even stated in the rules that the staff do not favor the idea of having multiple accounts. You can also always just play in another map. Here is what you can do next time a character gets stuck:
Go to the upper right side of the forum and click the "character reset" option.
It should look like this:
From there you log in again and then select either the "go home" or "reset home" option.
After that restart the game and log back into that character.