For years I too have shot both 20 and 30 minute targets between the different rimfire disciplines, and sometimes even Classes (Unlimited vs. 3-Gun). But, since I too am a 29 to 29:50 minute shooter, I much prefer the longer. Having said that, I shot my best ever 3-Gun Agg. when shooting in an Outdoor rimfire Unlimited State Championship match when using a 20 minute clock: a 748-55x accomplishing my only back-to-back 250's yet. Now, take Paul Bendix, and you'd be talking about only needing 10 to 15 minutes, all the time. Too each their own, and we'll just have to go with the flow I guess.
And my thanks to both Bill and Brian for all that they do to help promote our sport.
Just my humble 2¢worth?
Dave