Originally Posted by cubewheels

30 to 60 seconds out of the saddle (OOS) is good enough.

How long you can stay OOS depends on your weight. I'm 118 lbs and ride my daily 15 to 20 mile hilly route almost entirely OOS. My max uninterrupted OOS is 7 minutes between traffic stops. I really don't know how long I can stay OOS (never rode outside the city yet).

I simply kept practicing OOS on the bike for as long periods as possible everyday on the hills. Eventually, I got good at it, I'm now doing it everywhere, including flats and downhills.

I assume you're already knowledgeable of the correct OOS techniques via youtube, etc. Shift to higher/harder gear, sway the bike against the downstroke, light hands on the bars....