It’s about 7 miles from the main road to the Fish Creek Trailhead. Depending on your vehicle, you’ll want to take it slow. You probably won’t ever go over 15-20 mph or so – not including going very slow around blind corners and over larger bumps. Took me 45 minutes the first time and about 30 minutes coming back and each time after that.
Hiking from the trailhead to Fish Creek Camp is about 2 miles or so. Will take most people a little over an hour.
As an alternative, you can save the long(ish) ride to the Fish Creek Trailhead and stop at the Aspen Grove Trailhead which is only about 2 miles in. This will add 2 miles (one – way) to your hike.
I’ve never hiked from there, but will probably try that way next time.