I don't know where you're getting this five hours a day.
I see some people on the entire time I play, and at many times that can be up to 8 hours on weekdays. Weekends, it goes well past 12 hours at times (I do a lot of computer work in other windows

)
The hourly rate will cost players more money. I also agree that it would hurt the playerbase more than improve it. The MMO market is filled with the monthly pay-to-play model. Graal should be no different in this matter, besides maybe a lower monthly rate than those other games.
I can understand the concerns of the casual gamer. The pay by monthly plan isn't the best in the world. It best suits all the players across the board, however, while a pay by hour plan would only benefit a minority.
Perhaps an optional plan added would be good, but for now I would greatly prefer the current way payment and subscription is handled rather than this proposed idea.