It's worth mentioning that hydrometers are notoriously inaccurate (yes, you can get an idea how to adjust after checking the SG of water). But in the real world being a point off doesn't matter so much as knowing the beer is done.
I would never leave a hydrometer in a brew bucket, but only out of concern that the hydrometer may break.
I take multiple readings (usually) but if the krausen has fallen, the beer is clear, you've hit the upper range of the yeast's recommended temperature range, and the FG is around what it should be, I call it done. And then give it two or three more days, just in case.