Timing

"We're out of time so we have time for one more question."

If you're out of time, you don't have time for one more question. Out of time means no more time, not some indefinite time for a question you don't know.

Along with working in a meeting and arriving late to a meeting (because you were too lazy to show up, not because some unavoidable occurrence happened), I find deliberately causing a meeting to run over time even though you know you're doing it, disrespectful to the people who have the space booked after you.

If you're out of time, you're out of time, end your event. Follow up with email or schedule another meeting, don't run it over.