On our change process, we have two fields viz. Change Start Date and Change End Date.
We want to send email notifications to certain groups at 30%, 50% and 100% intervals based on the difference between the above two dates.
These notifications need to be sent only when the change has not reached completed or end state. If the change has reached completed or end state, whatever leftover email notifications are there from the above intervals, they need to be deactivated and not triggered.