<<"I'll be in Milan on 10&11 May and Switzerland from 12-16th May">>
Hi Yanti -
It is certainly possible to see some of the high alpine scenery near the Jungfrau then, but it is low season, so many cableways will not be running, and trails at higher elevations above approximately 2000 meters will likely not be open due to snow. The cograil train , including Jungfraujoch, will be running. Some hotels will be closed. The lower valley trails in the Lauterbrunnen Valley will be open.
and link to Jungfrau included on that page
In planning your journey, you might check -
You will find that a map combined wit the timetable can help you learn about distances and travel times, and will help to understand the routings that will be mentioned-
Coming from Milano, you can come through the Simplon Pass via Domodossola and Brig,thence to Montreux or to Interlaken via Spiez. A fair amount of interesting scenery, depending on which exact routing and destination you choose. I used to use it from Milano to Geneva regularly.
Coming north through Lugano and Bellinzona then over the Gotthard Pass to Luzern would be my preference. The scenery is striking, and it takes you easily to Luzern. You can do it all by rail, or, depending on timing, as well as the lake boat schedules, use the Wilhelm Tell Express route which you can follow on your own at different times from the official "Express" if you prefer. The boat is a lot slower, but quite scenic, and could always be used on a day trip from Luzern.
If you have not been to Switzerland before, Luzern is an excellent starting point, and a base for some other day trips.
By the way , I tend to use "Luzern" which is the German spelling, because Luzern is in the German speaking region. That is what you will see n the signs in and near Luzern.
The French Lucerne, English Lucern, Italian Lucerna are all the same place. ;-)
From will you return to Italy, or go from Switzerland to some other country. Do you know what city you will leave from?
That's a start.