Here's a diagram which should make Bert's explanation more clear. Posting here as I cannot add pictures to a comment.

When talking about timing in the context of swarming, it's important to distinguish the time for one specific element to swarm and the timing for a group of elements to swarm.

Since bulk swarming will be the main use case, its focus is there. Element startup time is not relevant for a swarm action so its excluded: once the element is starting up, the relevant agents can already coordinate the next swarming element.