The 9.8 km ride there takes about 30 minutes of riding time, add time for traffic signals.
If you haven’t been to the observation deck at the De Young Museum (closed on Mondays), a quick stop by there can preview the weather and the route on the big map. If you want to skip the De Young, you can cut off some time by taking the first right after passing the Conservatory of Flowers (the huge greenhouse) just after you enter The Park. That adds a bit of a slope, but not a big one.
Click this link for flattest route to get there. Make sure you ask google for directions by Biking.
Click this link for the flattest route to get back home. Make sure you ask google for directions by Biking.