Where in the pip-boy can I see how many "game days" have I played?

I don't think that's possible. But I do know that you exit the Vault on August 17th, 2277. Hit the Wait button to check the current in-game date, and figure out how many days/months/possibly years have passed. (It's up to April 2280 for me.)

Sorry if this doesn't help. It's the only way I know how to check to see how much time has passed.

Well, it helps if there isnt another way. I have DarnUI and the current date is displayed on the corner. I remember it was displayed in the inventory in Oblivion, with other statistics like current quests, ended quest, creatures killed, horses owned, portals shuted, potions made, days being a vampire...etc.

Thanks.