In the present Shortcuts implementation, we have the ability to set Actions for device groups. We do not yet have the ability to set Event Automation for device groups (eg. “all contact sensors of group become clear” or “any contact of group opens”).
There is a Wishlist topic that covers this request:
Please hop over and vote for and/or comment on it.
Presumably, on/off status changes of the plugs will be included in the available Shortcut trigger set when they are released. If they match what’s available for the bulbs and sensors, it will include “plug has been on for X time” and “plug has been off for X time”. Unfortunately, I’m not able to check that in the app yet.