Luzern/Schilthorn /montreux in a day?

Yes, leave Lucerne at 6:30 in the morning, get to Schilthorn at 10:30, take 10 pictures and have a cup of coffee, ride back down and get to Montreux by 4:13 PM.

Heidi, While that trip may be feasible, that's going to be a long and tiring day. Not something I'd ever want to do. You didn't say what time of year this would be taking place. That will have a bearing on whether you have daylight available for the last part.

Here is where the schedule is. For the Schilthorn-Montreux leg, enter via Zweisimmen or you'll be routed via Kandersteg and Brig. http://www.sbb.ch/en/home.html

I have to laugh when I read questions like this! There are many things that are "possible" but not practical. This sounds like a Chevy Chase Vacation movie.

Ken makes an excellent point...when do you plan on going, as the amount of daylight hours will affect your ability to accomplish this. The other significant factor is the weather..if it's clear, great, if it's raining or a lot of low cloud cover, your views will be significantly diminished.
I've travelled from Luzern to Interlaken-Grindelwald-Kleine Scheidegg-Jungfrau and return to Luzern in one long day( this was done in mid Sept 2009 ). I left Luzern on the first train in the morning( either 6:00 or 6:30 I can't remember , and was on the 8:00 or 8:30pm train from Interlaken back to Luzern ( arrived back in Luzern around 10:30-11:00 pm ). Like I said, it was a long day, but I didn't feel rushed, and I had time to take in the sites. Having visited the Schiltorn last month( stayed in Murren), my feeling is that the logistics of getting from Luzern to the Schilthorn is not that much different than getting from Luzern to Jungfrau. So, based on my experience, what you are suggesting is doable but you have to be out of Luzern on the first train, and you need to be mindful of your time

Our trip would be this coming Sunday, 4/11/12. I know it's a crazy idea, but it's either that or not at all. I am checking the weather and, as much as you can know a few days ahead, I am taking that into account. I know it will be tiring - but as my mom, who is going as well says, "you can sleep when you're dead" :). I just didn't know if it was logistically possible to leave Luzern bright & early, actually get up the Schilthorn, and be able to see Zwei-Montreux in daylight.

This weekend huh? Well, the days are getting much shorter now, so the likelihood that you'll have daylight from Interlaken to Montreaux is debatable. I guess it will depend on how much time you spend up in the Berner Oberland. Personally, I wouldn't be overly concerned about whether the journey from Interlaken to Montreaux is in the dark or not ( although I'm sure the scenery is beautiful). If it's stunning mountain scenery you want to experience, you'll have your fill of that in the B.O. for sure. And no, it's not a crazy idea IMHO...I did it from Luzerne for much the same reason in 2009, it was either that or not see the B.O. at all( at least on that particular trip). I don't regret having done it, and had a fabulous day( luckily I had a sunny day ). And I'm with your Mom, you can sleep when you're dead...lol
Make sure you get off at the correct train station in Interlaken....you want Interlaken Ost, not Interlaken West