I currently have several simple automations that I only use during Christmas & Halloween running. They turn some interior and exterior lights on at sunset and turn them off several hours later.
If I find a hub update available after the lights have turned On, will I disturb the Off time if I do the update? I'm wondering if I should do an update now or wait until the morning when there are no long term actions in progress.
What are they set up as? Simple Automation Rules? If so, no a hub reboot -- including one for platform updates -- will not erase scheduled jobs, as the time-based pieces of that app (and most similar ones) will be. So, all will be good as long as your hub is back up by the time the job is supposed to execute.
Understanding how actions are scheduled is one of the big keys to understanding Hubitat's automation capabilities. It's something that can easily cause confusion for newer or lighter users. Some of Hubitat's basic apps appear to work similarly, but actually operate differently.
Think about a light schedule like yours. Something like turn on at sunset and turn off at 11 pm. If you use the Basic Rule app your trigger is sunset and the turn off event is only scheduled when that original sunset trigger happens.
If you reboot your hub between the trigger and off times your lights will turn off according to schedule. If you reboot your hub around the sunset and you miss your trigger your lights won't go on. Nor will your 'off' be scheduled. So if you notice the lights not turning on and turn them on manually they will not turn off automatically.
Here's a bit of a gotcha. If you use the Simple Automation Rules app as @bertabcd1234 describes the lights will still go off if you reboot your hub while the 'on' was scheduled. That's because the 'off' is also scheduled when the app is created. The events are scheduled independently. You wouldn't know that by looking at it, it seems similar to Basic Rule. (It seems like there might be a small bug in the app. The app appears to require an 'on' event to happen once. After that it works as I describe, no 'on' event required to get the 'off' to trigger.)
If you are scheduling switches based on times there are at least a couple good user created apps that make the process easier to visualize. This is the one I use, on and off are scheduled independently: