Without searching to see if this problem is well known, I thought I'd post it for others.
One of our systems backs up at 2am. 8 databases, total about 150GB, backup takes just over an hour. Uses Standard SQL Server maintenance plan. Only keeps the most-current backup; deletes older files.
Sunday morning's backup, with the time change, didn't go well. It ran at the "first" 2am, in just over an hour, but the Duration in job history instead of being 01:06:25 like usual, was -3976.20:09:23 (whatever the heck date/time that represents).
Then it ran again at the "second" 2am after the time change, but it didn't delete the previous backup files (I presume because their time stamp of say 2:45 am was newer than the time the job was running). So our backup drive filled up and everything ground to a halt.
It's a once-a-year problem and it was easy to fix. But I suppose based on this I'd recommend avoiding running backups or other SQL jobs between 2am and 3am. ??