This statement about summer skiing and snowboarding from the Zermatt website.
The summer is here and the sun is high in the sky – but up on the Theodul Glacier above Zermatt the conditions are wintry and still suitable for skiing, snowboarding and freestyling up to midday. So: rise and shine!
Note key phrase "up to midday". By the time you get there, rent equipment and get up to the glacier, it is likely to be closed because it just gets too slushy to keep the pistes open. So if it is really a bucket list, I would go the night before and get up there first thing. And check if the Ikon pass is valid for summer skiing/boarding.
https://www.matterhornparadise.ch/en/experience/skiing/summer-ski
You could stay in Taesch the night before if you are looking for bargain lodging.
PS. I guess if you left Interlaken Ost at 5:59, you could get to Zermatt by 8:17. That would give you enough time to rent equipment and snow board until midday.