Aug 17, 2020 - 12:27 AM
If you want to do all 3 in 1 day, stick to your original plan. Train to Wengen, cable car to Mannlichen, walk to KS, train to Jungfraujoch, return by train and get off at Eigergletscher station, walk the Eiger trail to Alpiglen, train to Interlaken either by way of Grindelwald or back the other way through Wengen.
Approximate hiking times are Mannlichen to KS 1.2 hrs, Eiger trail from Eigergletscher to Alpiglen 2.50 hrs. So it depends on how much time you spend at Jungfraujoch as to whether you can do it all in a day. I have hiked most all the trails in the Jungfrau area but have never been interested in going to Jungfraujoch (touristy, expensive, and often crowded) but reportedly some people spend most of a day there but typically a half day is common and i expect you could spend less.
If you should decide on splitting it between 2 days then pkerr’s itinerary is fine. I would encourage you to hike from KS to Eigergletscher (1.20 hrs). It is short and moderately steep but in my opinion it has an especially nice view of Jungfrau and Monch up close and pretty valleys on either side.