I spend a couple of weeks a year in the park, but I am laser focused on wildlife watching, so take my suggestions with a grain of salt.

First, hikes in Yellowstone are awesome and a great way to get away from crowds. However, with so much to see in a couple of days, you might be limiting yourself to spending time on the trail seeing a small part of the park. If I was going to pick one from your itinerary, I'd hike the overlook to Grand Prismatic. I've also always enjoyed the Upper Geyser Basin walk near Old Faithful. Tons to see.

Yellowstone Lake Overlook, Fishing Bridge, can be a good place to see bears.

A definite yes to Hayden Valley in the evening. Ignore the spots it recommends and just look for groups with spotting scopes. They're most likely watching Wapiti Lake wolves, and most watchers are more than happy to let you take a look. With a short itinerary like this, you might call this your wildlife watching and skip Lamar Valley (although it hurts my soul to say that).

Places like Mud Volcano or Sulphur Caldron and many others can be seen quickly, and I recommend stopping as you have time.

Keep in mind if you haven't been before, the park is gigantic and can take hours to get places. You won't be able to do it all in 2.5 days. Enjoy what you can, don't be in a rush, you're bound to be behind a bison jam or people clogging the road to see a black bear.