Assuming the unstated requirement that you want your cron job to only run once per day, scheduling for 3 am is not a software problem. It's a lack of understanding by the person problem. By definition times around the time change can occur twice or not at all. Also, in the US 3am would never be a problem as the time changes at 2 am.

Also, naming things, cache coherency, and off by one errors are the two hardest problems in computer science.