The Remarkable (the older one that I have; not sure on the newer one) has two "off" modes: an "inactive" kind of mode, where it has just deactivated the screen from lack of use, and a "sleep/power-off" mode, where it's actually either gone to sleep or been powered off by the user or a low battery.

In the first mode, it comes back in about 1 second. It's enough that there's a bit of a lag and I don't like it if it happens right in the middle of something, but I haven't run into this very much.

In the second, it takes a few seconds to spin up, so I got into the habit of doing that before a meeting or whatever started. It takes about as much time to get it started up and navigate to the appropriate file as it would to fish a binder out of my bag and open it up to a blank page.