It's a little bit insidious. They do. But if you do a lot of recording you won't see that for extended periods of time. But it will suspend sooner or later and then you get to play with the gremlins. Unless of course you got all your cron syntax right on the first go.
yeah right, first go (much hysterical laughter)
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edit: in all fairness it's a good point. Cron will be a pita if you let the Kindle sleep. It shouldn't be a problem for a device that can be tethered to an outlet. But it's worth thinking about what to do on a device that you let sleep. Perhaps a clock display, when not plugged in should be designed to "time out". And redisplay/update only after the Kindle wakes up from some other event.
@handyguy
Here is a thread with useful information about both using python to display screen objects and sleep(ing) cron dragons.