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Hello, are there any other wires in the back of the box other than what is connected to the old switch?
No, you will need to make a pigtail from the white bundle to the new timer. You will want to connect the black going up to the light to the red of the new timer switch. Power black from the old switch to black on the timer. White from timer to whites in box that pass through in the back. Grounds (green and bare copper) together.
if you don't know what a pigtail is see the picture I've uploaded
You mean a white wire goes all the way through your box without a wire nut splice? Do you have conduit and wire or romex cables?
ah ok, is there a loop in the white or enough slack to cut it in the middle? You will definitely need a neutral connection to make this timer work.
what do you mean wiring to the box?
No, that's a code violation for neutral current to be run through the equipment grounding path. My recommendation is to get the T-tap, or see if you can pull some slack from the light fixture so you can splice at the box. Also, you could buy a length of white wire and pull a new section from the fixture to the switch box using the old section as a pull wire. You should be able to buy it by the foot or in short rolls at a hardware store.