Step 1: Understanding the Question:
The question asks for the precise engineering definition of dwell time in tablet compression.
Step 2: Key Concept:
In a rotary tablet press, each punch pair moves through a defined cycle of filling, compression, dwell, and ejection as it passes under the compression rollers.
Step 3: Detailed Explanation:
Dwell time refers to the brief interval during which the punch head stops its vertical travel and stays at maximum penetration into the die while it is pressed between the punch head and the curved surface of the compression roller. This is the moment the compaction force is actually transmitted to the powder bed to form the tablet. Ejection, described in two of the other options, is a separate later stage where the lower punch pushes the finished tablet out of the die, and it happens away from the compression rollers, not under them.
Step 4: Final Answer:
Time it takes for the punches to stop moving vertically and achieve maximum penetration in the die under the primary compression rollers.