While there are logistical issues with shorter presentations at multi-track physical events, I've come to think that 25-30 minutes is a better sweet spot for conference presentations than 45-50 minutes. (With the exception of workshops/tutorials in most cases.)

And it's where I've ended up with my podcasts. Less than 12 or so feels like you're barely getting started and get past about 30 and, as a listener, I'm generally losing interest. It's no coincidence that longer professionally produced podcasts almost always have segments or otherwise break up the content.