Tickets for Jungfrau or Schilthorn

There isn't any need to purchase tickets for the Schilthorn in advance. I can't comment on the Jungfrau.

Time is pretty relative depending on what you want to do. To get to the Schilthorn you are either going to take the cable car/railway to Murren and then another cable car up to the top or go further down the valley and take cable cars up to Gimmelwald, then Murren, then a cable car up to the top.

There are so many interesting places to stop, hike, eat, or look at on the way up or down that I would plan an entire day and still not have enough time to do it all. Your trip will include Murren and it would be a shame to just ride through it without stopping.

Suggest you not buy tickets in advance. There are days when the weather is great and the views are spectacular. Other days the opposite is true and you can't see a darn thing.

No No No - never buy these tickets in advance. Buy them the morning you want to travel. Check the weather on top before you buy the tickets. If it's cloudy with no view or rain or blizzard - you definitely don't want to go.

Thank you for all your input on the tickets! We are looking forward to our Swiss trip. BTW is Bern worth visiting while we are close by?

Some people who only have one day make it up to both the Schilthorn in the morning and Jungfraujoch in the afternoon, but if you're staying longer, give them separate days, so you can make more stops on each side of the valley. Bern is a good bad-weather day-trip option. Otherwise, I'd make sure you completed what you wanted to see around Lauterbrunnen before visiting the city.

most people prefer to be in/near the Alps so maximize your time in Lauterbrunnen.

If you want to do a city, Bern is a good choice. Nice size, pretty, stuff to see and do, walkable, good trolley system, pretty good set of dining and shopping options in train station. And bears!