Never mind how fast you go. The question is about length of ride not how fast you go. If someone wants to raise a new poll about average speeds. Go ahead.
I think this is the confusion. The question is about a
time but here you are talking about a
length which is normally thought of as a measure of
distance (although you can of course also talk about a length of time).
The thing is you can't talk about any factor in isolation. Riding 200 miles sounds a lot, and if you did it in a day it would be, but it you did it in a year, it isn't. Similarly you could ride for 30 minutes in such a leisurely way that your heart rate would barely change. Or you could push yourself to your limit for half an hour and be absolutely wrecked. For any of us a ride is a function of time and effort, and how those two combine our fitness and the terrrain.
I guess we're talking about an average kind of ride - in which case I'd say it's all I have time for in the week most weeks, and as I am at peak un-fitness, live live in a hilly area, and seem to have much less power post-COVID, half an hour is plenty, and I'm not entirely comfortable with the narrative / suggestion that half an hour of riding isn't worth it, or isn't 'proper' in some way. Short journeys by bike are what we as a community (of forum-ers and as citizens of the earth) should be encouraging rather than doing anything to in any way imply that a 'short ride' - however defined - is somehow less worthwhile.