In many time zones, Daylight Savings Time (DST) will move the clock forward one hour in the spring and move the clock back one hour in the fall.
During all parts of the year, your action will execute at your selected time of day according to the rules of your selected time zone.
In the winter, your action will execute at 3:30am
In the summer, your action will still execute at 3:30am
In the spring, when Daylight Savings Time moves the clock forward, there is an hour that does not exist. Many times this is between 2am and 3am.
If your action would normally execute during this time period (for example, at 2:30am), then it will execute at the new 3:30am.
In the fall, when Daylight Savings Time moves the clock backward, there is an hour that exists twice. Many times this is between 1am and 2am.
If your action would normally execute during this repeated hour, your action will execute only once. For example, if your action is scheduled to execute at 1:30am, then your action will execute at the first 1:30am only.
The exception to this rule is if your action executes using an "hourly" schedule. In this case, your action will execute at both 1:30am times.