7 days in Switzerland Itinerary help

What time of year?

Hi,
We are planning to travel around last week of May or First week of June.

Your itinerary is very day trip heavy. For example, to do the Golden Pass to Montreux and back is going to be almost 7 hours of train in one day, Jungfraujoch another 3, Zermatt, another 5, Grindelwald First another 3....You basically have 2-7 hours of train commuting every single day. With 8 days I'd narrow down your scope a bit and just enjoy the places you're going. And nix Rhine Falls & Lindt - in the grand scheme of things they're really not that great. Something like...

Day 1 - Head to Montreux from Zurich, stay 2 nights, explore town
Day 2 - Chateau de Chillon
Day 3 - Golden Pass Express to Interlaken, continue on to Wengen for 3 nights, explore Wengen
Day 4 - Jungfraujoch in the morning, Eiger Express down to Grindelwald, then First/Bachalpsee in the afternoon
Day 5 - Lauterbrunnen + Murren + Schilthorn
Day 6 - Boat ride on Lake Brienz with your luggage from Interlaken to Brienz, continue on train to Luzern in the afternoon, stay 2 nights
Day 7 - Rigi
Day 8 - Luzern > Zurich to fly out

Or if Lindt/Rhine & Zermatt are non-negotiable, then skip Montreux and do something like...
Day 1 - Head to Zermatt from Zurich, stay 2 nights, explore town
Day 2 - Zermatt/Gornergrat
Day 3 - Train to Wengen for 3 nights, explore Wengen
Day 4 - Jungfraujoch in the morning, Eiger Express down to Grindelwald, then First/Bachalpsee in the afternoon
Day 5 - Lauterbrunnen + Murren + Schilthorn
Day 6 - Boat ride on Lake Brienz with your luggage from Interlaken to Brienz, continue on train to Luzern in the afternoon (store luggage to explore), then continue on to Zurich, stay 2 nights
Day 7 - Rhine Falls/Lindt
Day 8 - Fly out

Wanderweg has given you some great suggestions.
Push the trip into June as much as possible, as many of the lifts and trails aren't open in May.
Give yourself flexibility for weather variations, especially in the Alps. You can't decide you're going to a summit until the weather forecast, the day before. Most summits have cameras, and you can decide check online that morning if it's clear. Most summits are clearer in the mornings.
Have a great trip in this beautiful country . Safe travels!