No one is getting paid to make these podcasts. You have to remember that!
I think the more content the better! Everyone likes something different.
If you think there is a market for a 10 minute podcast when start one up, there isn't a big barrier to start doing it.

I would love to make 3 x 30 minute podcasts a week every time something happens. The reality is that there is editing, there is recording, if there is more than 1 person you have to schedule it in, etc.
I listen to most podcasts at 1 to 1.8x speed depending on how long my trip is that day or how slow/fast the person talks.

Bam! There it is.
Shorter = More thought has gone into it, which in turn requires time!

There is a Mark Twain quote for almost everything.