Well I read the OP checked out the route on Google maps or map quest.... but I'd say you better drive it to see if there is any significant climbing along the way. That could make a big difference. With that said, it's definitely doable.

I ride a 60 mile round trip commute on my single speed cyclocross bike (a Surly Crosscheck) to or three times a week. My ride is basically 10 miles of slight downhill, followed by 10 miles which includes two good climbs and descents, and ending with another 10 miles very slight downhill. It takes me about 1 hr. 40 min. to ride to work, and about 2 hrs flat to get home - more if I get nailed with a headwind.

Now even though I ride a single speed (42/15, about 75 gear inches) I run 28 mm wide tires on a bike which weighs 24 lbs before I load it up with water, lunch lighting and clothes. It's not road racer light, but it's not a tank either. If you're talking about a single speed beach cruiser that weights like, 35 or 40 lbs., you better allow 2.5 or 3 hrs each way. Drive it first. Then take the fast bike with a good lock.

DanO