I'm running the latest 7.1.5 Beta version and I do not see any way to accomplish this as of yet. This may be a good feature.
Not necessarily a central time exception for 'all in the group' due to the likely major changes necessary to do so, but maybe a simple right-click the group and have an option to add a time Exception to the selected jobs... .after which you'd have to manage individually if you wanted to remove that exception.
Brian