The minimum we’d recommend is 1 minute, but arguably it should be longer still. It’s not so much a question of relability as design intent- epaper was never designed to be refreshed at a high frequency, and thus there are lots and lots of drawbacks from attempting to do so. Have you ever used an ebook reader, and noticed how every few pages it will invert the whole screen? That’s a compromise found even at low refresh rates to prevent the build up of image retention and other display artefacts.
It’s certainly possible to update monochrome epaper at a high rate, but since you’re physically moving particles of ink you can’t really beat the physics and avoid any lasting damage. We haven’t subjected our displays to anything more than 30 second intervals for tens of thousands of cycles- so we just don’t know what might happen.
I suspect nobody has pushed a Papirus to the limits long enough to notice any drawbacks and the same applies to our displays. You may be fine, but there’s no telling for how long.
You’ll probably get bored of or replace/rebuild your project before you manage to damage the display, but I’d recommend an OLED or small LCD since at higher refresh rates you’re not really playing epaper to its advantages.
Here’s an interesting video about pushing these displays to their limits: https://www.youtube.com/watch?v=MsbiO8EAsGw