I will be staying in Murren and plan a trip hiking from Mannnlichen to Klein Schweidegg, then taking the train to Jungfrauloch (then traveling back to Murren by train/lift/etc.). Considering a leisurely pace on the hike, is that plan too much to do all in one day? That is, will there be time to visit Wengen on the way back, and will I have to be concerned about the trains/lifts shutting down if I'm late? The last thing I want to do is hurry through the day. Thanks!
It can all be done in a day with an early start in the morning with no need to rush anything. Wengen would be a good place to have dinner. The lifts up to Murren run until about midnight or so.
I have just been to the Jungfraujoch in May and would recommend that you start your day by taking the first train up to Jungfraujoch. This has several advantages, the price is cheaper, the views are normally better in the morning, and it will not be as crowded as it will be later in the day. This way you can get back around midday and will have enough time for hiking and other activities in the afternoon
Problem with doing Jungfrau first is that you will have to hike in the opposite direction from Klein Schweidegg to Mannnlichen, with the mountain peaks to your back. Jungfrau is a big complex and crowds are easier to deal with compared to smaller attractions like the Schiltorn.