Even on a tight schedule, Eiffel Tower at Night / Sparkle earns the hours.
Allow 30–60 min.
On the hour after sunset, the whole tower erupts in twinkling lights for five minutes — best watched for free from the Champ de Mars lawn or Trocadéro with a bottle of wine. It's the romantic, no-ticket way to 'do' the Eiffel, and arguably the better one.