To improve power efficiency, Android now batches together alarms from all apps that occur at reasonably similar times so the system wakes the device once instead of several times to handle each alarm.

If your alarm is not associated with an exact clock time, but it's still important that your alarm be invoked during a specific time range (such as between 2pm and 4pm), then you can use the new setWindow() method, which accepts an "earliest" time for the alarm and a "window" of time following the earliest time within which the system should invoke the alarm.

If your alarm must be pinned to an exact clock time (such as for a calendar event reminder), then you can use the new setExact() method.