Thank you for your feedback. Please let me give you a specific, and a more general reply.
Please don't expect specifically this feature. PRTG allows to group objects, this could be used to apply a schedule on a group which then in turn pauses all child objects. Of course, this approach is of little help if the set of groups/devices which are undergo a maintenance changes. But to keep the user interface clean, we intentionally don't add too many options.
Generally, we overhaul each component of PRTG. This is an ongoing process we take one step at a time. We are collecting user feedback like yours to learn what PRTG users want, and incorporate those requests in the re-design. However we are still having to focus, and cannot factor in any single request.
The PRTG API allows some control over a PRTG installation with scripts. While it involves some manual work to write a script for this, you can pause/resume objects with the PRTG API. Have a look at the integrated API documentation in your webinterface, /api.htm?tabid=6