The ride itself would be about 15 minutes, but...
Since buses run continuously and not on a timed schedule, if you miss the last bus by a few minutes, you'll be waiting a while for the next one. So build in at LEAST 30 minutes for the ride. Another 15 for the walk to the restaurant, then you should also be at the podium before your ressie time, so add another 15... give yourself an hour.
If you arrive very early, see if they'll take you before your ADR time. If not, at least it's a nice spot to kill time!