I just spoke to Dell support about my issue and it is apparently a known issue with Europe\UK locales.  The similarity between our issues could be relevant - the workaround for me was to set the Locale\Regional setting of my PC from which I am trying to do this to US.  Not the timezone or any other settings, just in Control Panel, then "Region and Language" and then on the first tab, the 'Format' box needed to be set to "English (United States)".  Close browsers, start again and it worked for me. Could be worth a try if you're not already in US format. (mine was in UK).
Hi, I'm trying activate Business Hours -template from Virtual Storage Manager for one Datastore using vSphere Web Client. Everything else works fine, but I cannot change the time interval from Snapshot Schedule. It stays in 12:00 midnight to 12:00 midnight. I can't change it manually or dragging the bar.  I've tried with IE9, IE11, newest Chrome browsers. And with Flash 15 and 13 -versions. Same error.  I've added the URL in Trusted Sites with lower security settings - no help. Is there a bug or something else I can try?    
Virtual Storage Manager - Cannot change snapshot schedule time interval using 
vSphere Web Client