I've been to Ausable Chasm, and, yes, it was a lot of fun, in a retro-tourist-attraction sort of way. I mean, it hasn't changed much at all since the 1950s or 60s, and that's a good thing, it's very charming, and I remember our trip there very fondly.
So, yes, go, and yes, one day is plenty, and, yes, fall is a good time 'cause the leaves may be changing and very colorful and it won't be too hot, but I don't think they have bike trails, sorry.
Good luck, and the link below is to their official website...