Unit testing time-bound code

Question

I'm currently working on an application that does a lot of time-bound operations. That is, based on long now = System.currentTimeMillis();, and combined with an scheduler, it will calculate periods of time that parametrize the execution of some operations. e.g.:

public void execute(...) { // executed by an scheduler each x minutes
    final int now = (int) TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis());
    final int alignedTime = now - now % getFrequency() ;
    final int startTime = alignedTime - 2 * getFrequency(); 
    final int endTimeSecs = alignedTime - getFrequency(); 
    uploadData(target, startTime, endTimeSecs);
}

Most parts of the application are unit-tested independently of time (in this case, uploadData has a natural unit test), but I was wondering about best practices for testing time-bound parts that rely on System.currentTimeMillis() ?