How can I apply Rigid Body physics to a large group of objects?

Sadly, it’s not that simple.
In my scene, I have almost 300 shards from a cell fracture. I want to hold these shards in place, then activate them when an object comes to collide with them, preferably using a keyframe. But I don’t want to go into each shard and keyframe it independently.

How would one accomplish such a task?

Select all the objects, e then the active object and click here :