It is all about standing before the discomfort sets in for me. During Zwift rides I stand on many more short hills than I would in real life, trying to get at least a few seconds out of the saddle every 5-10 minutes or so just to relieve pressure and let the blood flow.
The timing is different on workouts in erg mode but as long as the power is at Sweet Spot level or higher, same thing - I stand for short periods. Can also do it during the low power recovery sessions.
If Zwift put in traffic lights that forced you to stop, could skip all the standing!