And the answer to your question - If you’re on a notebook, make sure that your hibernate time is less than your battery time. Otherwise, your battery will drain before the option can kick in.

My understanding is that hiberbate is a fully powered off state. The memory contents are written to disk and an indicator is set that indicates a hirenate state. When you next power up, the system goes to boot, but first checks the hibernate indicator, if it is set, rather than boot it restores your memory from the disk file. It follows that you should be able to safely turn off the power and remove the battery whilst in a hibernate state.

Contrast hibernate with standby where the memory contents are not written to disk (the system just goes to a low power state) and so all active processes and data in memory will be lost if you remove power.

I use standby quite a lot on my desktop PC during the day. Instead of taking about 80 secs to boot, it is up in a few secs.

But I always power down overnight anyhow. I don't take with the idea of never / infrequently rebooting. I consider it risky as, if changes have been made (e.g. software updates) that have destabilised the system, one wants to find out about it sooner rather than later as one is in a much better position to remedy such problems then.