Toledo has a lot of exhibits for its size, especially with the museum being open now. There might be 250+ exhibits total at this point, including some in unexpected places: feathertail gliders in the indoor kids play area, birds of prey in a shed behind the reptile house, small herps and invertebrates hidden in the oak forest room of the museum. If you like to see everything it might be tough to fit in Indian Creek on the same day. Detroit is a lot bigger in area, but the exhibits are mostly spacious, wide open yards so most of it can be seen relatively quickly. It should not be difficult to tack on Belle Isle, and if you hit Detroit at opening you might be able to tack on Indian Creek on this day. One other note -- if you like wildlife watching, Peregrine Falcon nest on the Detroit Zoo water tower and often hang around for much of the year, the pond in the middle of the zoo has Blanding's Turtle that might be basking if it's warm, and in mid/late fall there typically lots of migrating waterfowl, loons, etc. around Belle Isle.