Instead of "rest periods," one could use the antonyms "activity times" or "working intervals" to describe the opposite concept. These terms suggest a constant state of movement, engagement, and productivity, rather than a break or a pause from activity. "Active phases" or "busy stretches" are also possible antonyms, emphasizing the dynamic and energetic nature of an ongoing task or schedule. It is worth noting, however, that constant activity and productivity can lead to burnout, exhaustion, and lack of creativity, and that occasional rest periods are crucial for maintaining physical and mental health.