DHS in the Animation Building. See www.kenythepirate.com for comprehensive character info. Baymax and Hiro have never been published on WDW schedules that I know of.
From what I can tell, Disney isn't willing to commit to keeping Baymax at Magic of Disney Animation in HS, which is why he isn't listed on MDE. Still, he's very popular and there's always a line for him so although the original plan was for him to stay through March I think the plan now is for him to stay indefinitely. They might switch him out for Olaf during Frozen Summer Fun, though. That's the rumor, anyway!
This was my favorite meet and greet from our trip this February. They really did a great job with this one. You have to take off any pins or sharp objects before meeting him.
From my research, I learned he starts meeting at 10:30 , HS animation building. Get in line at 10am They will be around till further notice. This is at the top of my list for my boys next month. I'm looking forward to it.
We met Baymax and Hiro last week. The meet starts at 10:30. I got in line to hold our place at 9:50 while my wife and son went to some other characters. I did give Baymax a fist bump and he fluttered his hand up into the air. I heard they were only there until the end of March but that may have just been a rumor.
I haven't told my son about Hero and Baymax being there because I am worried they will be gone by our trip in September. Fingers crossed that they stay and my little ones get to meet them!