Charge playtime instead of days?

[googleman]

Doesn't look like it has been brought up before, but I have an idea.

What if Graal, instead of charging for days, charge playtime. This way if you go on vacation or sometime similar, you don't loose 7-20 days. This way have a certain amount of hours you can be online and be charged for playtime instead of days. What do you guys think? Personally I think its better for the players. What do you think?