Find out more about this problem and how you can test your iPhone's alarm after the break.
The bug seems to be affecting alarms that are set to sound every day, or those only set to go off once. And, according to Engadget, deleting and resetting the alarms does not fix the problem. While Apple is aware of this bug and says it's working to fix it, there's no ETA for a fix, so US users could face problems when it's time to "Fall back" next Sunday, Nov. 7.
To test your phone's alarm before or after the upcoming time change, set a one-time or daily reoccurring alarm to sound a minute or two from the time you set it. If it sounds properly, you're in luck. If not, you may want to consider a backup alarm just in case the bug isn't fixed in time.