I think your problem is more likely to be clouds. Any time of year the tops of the mountains are wreathed in clouds on many day - even if the valleys are clear. You need to check with the train station to determine the weather at the top before ascending - or you won't see more than about 10 feet. We had to wait 3 days in Interlaken (naturally touring other towns in the area) before we got a day that was clear atop the Jungfrau.

As for a shot of a particular glacier - I would look at a bunch of photos online to see if you can figure out the best angle for this shot.

If you are planning to view the Matterhorn peak from the Gornergrat there is a live cam view in the Gornergrat railway waiting room so you can see before you get on the train whether or not the peak is clouded over.

Thanks for the tips, what I really want to know is when (morning or afternoon) is the best time. I remember being in Canada going on top of a mountain on a bright day and I had clear pictures of a random valley but was not able to take a decent picture of the valley with the lake (which would have been picture perfect). I will have 3 to 4 days in the Interlaken/Jungfrau Region, so offcourse the weather report will be my number one guide for planning what to do when

I think the best way is to look at existing photos and see what compositions look interesting. For example google "Matterhorn pictures switzerland", "swiss alps pictures," etc would bring up many pictures of all sorts. I think the better pictures for mountains are usually taken very early or late but not in the afternoon when the ray illuminates the slope from the top and washes away the terrain contours. Of course, if you want to add foregrounds, you have to compromise the balance between the two. I try to see if I can capture the mountains at sunrise when only the top of the mountain is illuminated in warm tone.

Early or late---not mid-day.

But if the OP wants to see into the valleys, they'll be in darkness early or late -- depending on what direction the valley faces.

Another thought: the closer to the summer solstice, the higher the sun, the more you can see. So do this trip as early in the summer as you can.

"But if the OP wants to see into the valleys, they'll be in darkness early or late -- depending on what direction the valley faces" ... that's exactly what my problem is I don't know what time of day to have the right direction (sun behind my back) to the best pictures ...

Well, if you know which valleys you want to photograph, you can look them up on a map to see which direction they run. Then pick the right time of day to have the sun behind you.

If these are digital pictures it's called Photoshop.