Have you noticed that the best facilitators always seem to complete their sessions right on time? They don't have a crystal ball that enables them to foresee exactly how long each step will take. Instead, they use a few facilitator tricks to manage the timing and pace of their sessions.
When preparing for a meeting, working session, or interactive workshop, I try to estimate the "right" amount of time to allocate for various discussion points or exercises. But as any experienced facilitator knows, "stuff happens" and I often find that the session progresses faster or slower than anticipated.