I am not sure I understand. why that would be important.
A group creation is not part of any animation and does not need a keyframe.
It is a group(div) on the scene at some position. It is there or it is not and present as an element on all timelines like any other element. ( which also do not have keyframes to indicate creation)
You can change that position and animate the group properties including position with keyframes.
Elements within it are in there at some position which can be changed via keyframes…
Saying all that having an event for element creation would need hype to be able to create/add elements on the fly, something we have asked for in the past. But more in the vain of cloning.