Overcast says its Smart Speed feature has saved me 30 hours (over the last ~5 months), so I expect it to save me 100 hours within a year. It is especially useful for podcasts and language learning material with a lot of pauses, but I have become used to it, and so I now keep it enabled for most audiobooks that I load into Overcast just to get the dynamic playback speed.
I'm at 173 hours! I've liked Overcast (I've been a premium customer for two years), but I find myself wishing it has better features now. It feels like it was the best a couple years ago but hasn't done much since. Smart Speed is the one thing that has kept me from switching to something else so far.
296 hours myself. I have also been pleased with Overcast until just recently. Now that I am stuck at home, I went from listening to all my podcasts from my phone to listening to most of them from my computer. Overcast's lack of desktop app and pretty poor web interface are causing me to consider switching for the first time.