I would say that 20 minutes is really close to the borderline; it may be enough to warm the engine oil properly and it may not be enough to do so, or it may be enough under some driving conditions and not others.
Do you have a proper direct reading oil temperature gauge in the vehicle? Could you install one, even temporarily?
Generate your baseline by noting the stable temperature each vehicle reaches in your 45~60 minute commute (or a similar drive if you've already moved). By getting your target oil temperature this way you eliminate issues around such things as exactly where you are measuring the temperature (and is why I'm not suggesting a certain temperature which would be "OK").
Then see if you are able to reach that baseline at least most of the time in your shorter 20 minute commute.
I would also want to mention that you really don't want the oil to *just reach* the target temperature as you roll into the parking lot at work ... ideally the oil will spend some time at the target temperature to cook out moisture, etc. It doesn't happen instantly.
If you do have issues getting the temperature up, I would suggest incorporating an oil heat exchanger (is that the correct term?) whereby the engine oil is both heated and cooled by the engine coolant. It serves two purposes; it brings the oil up to temperature sooner, and then removes some heat to achieve a desireable, stable, hot oil temperature.
Some OEMs use them; I know VW does, and my Miata has one. Or, some Automatic Transmission-equipped vehicles have transmission oil "cooler" lines as part of the radiator, but they are essentially the same thing, ie they warm as well as cool. You might be able to add an aftermarket transmission oil cooler (which usually work very well, better than the rad cooler setup) and then use the rad cooler lines to warm/cool/stabilize the engine oil. If you have a manual transmission, which will not have it, you can sometimes swap in an auto-trans radiator that has the feature.
