Allow at least 2 hours to ascend the Eiffel Tower. You have to queue for quite a while to get to the first lift. (I'd expect a queue of somewhere between 30 minutes and an hour, this Saturday, if you go in mid-afternoon). Then, when you get to where that lift takes you, you need to queue again (although probably only for around 10 to 15 minutes) for the second lift, which takes you to the top. After spending some time at the top, you'll need to queue for around 10 minutes for the first lift back down, and then for another 10 to 15 minutes for the lift back to the base.
By the time you've taken a few photographs, you'll probably look at your watch and realise that you've been there for over 2 hours.
The best photos of the Eiffel Tower are taken from the other side of the Seine. Cross the Pont d'Iena (which is alongside the Eiffel Tower) to the impressive Palais de Chaillot. You can get some great shots of the Eiffel Tower, with the palace fountains in the foreground.
If you're including the Eiffel Tower in a tour of some of the main tourist sites, you might like to know about the Batobus. It's a hop-on, hop-off river service which runs between Notre Dame Cathedral and the Eiffel Tower. (The full journey takes around an hour). It's a great way to see some of the main sites and, because yo purchase a day ticket (for unlimited travel) you can get off and visit anything which grabs your attention:
http://www.batobus.com/english/8escale.htm
To link between the Eiffel Tower and the Arc de Triomphe (and the Avenue de Champs Elys�es), take Metro Line 6 from Trocadero (alongside the Palais de Chaillot) to Charles de Gaulle Etoile.
Chris