Installing switch with timer
I'm surprised that the box or paperwork that came with the switch didn't have instructions, so here is my advice (25 years as an electrician):
The black wire goes to the hot bundle, the green wire is ground, and the blue wire goes to the light that is being switched.
If there is a pig-tail that acted as an individual wire to the old switch, you can either keep that and attach the black wire to it, or remove it from the bundle and connect the black wire on the switch directly to the bundle.

As a way of checking what I am telling you, on the switch itself, there may be some labels for each of the wires (the black, blue and green wires).
Typical labeling for the 'hot' wire is: "Hot", "Common", and "Line"
Typical labeling for the switched wire is: "Load", "Line", or "Switched"

Note that in my experience, whenever the label for the Hot wire is "Line", the switched wire is never called "Line" -it is almost always labeled "Load" (which is more accurate -but let's not argue semantics).

Good luck and happy wiring!

:)
Greg