Paris did not like us and we were only there for 5 days. Our final half day was a tour of the Eiffel Tower. The guide was lovely and he was Canadian. We got to the second level and we were having a a look at the great view when some security people started to put ropes across section and you were not allowed past them. The guide found out that a package had been left lying around in other words a bomb scare. We were not allowed to access the lifts and the people at the very top had to stay there. We were asked to leave so we had to walk down the steps in the rain (which only started when we started to walk down the steps,) and it took us 20 minutes and when we reached the bottom my legs felt like jelly. But to answer your question it is probably about 15 minutes.
Marg