Then when the screen turns on it'll morph from the old time to the new time over the course of a second or so - that's expected, and the idea is it's meant to look nice.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Do you know what you're doing when it is 1 hour behind? If you're using the default (Morphing) clock: https://www.espruino.com/ide/emulator.html?codeurl=https://banglejs.com/apps/apps/mclock/clock-morphing.js&upload
Then when the screen turns on it'll morph from the old time to the new time over the course of a second or so - that's expected, and the idea is it's meant to look nice.