+600mb? How many hours this VN have? (Just asking to be prepared...)
It's been a bit since I played the game through in its entirety, but I remember taking a couple of weeks reading it for between 2-4 hours a night. I would say there is at least 30 hours worth of reading material, though its probably close to 40 if you play all routes and try to get all the endings.
Going through one route though should take between 8-10 hours, with subsequent playthroughs being shorter as you can skip over the first 2.5 days, until you reach the point the story initially branches.