I am trying to replace single pole switch with a programmable timer switch. Leads (black and white)on the single pole switch measures 25 volts while bare copper in the back of switch and white (neutral)measures 125 volts. I was planning to attach black from box to black of timer, green of timer to bare copper for ground and white of timer to white of box and cap the red by itself with a wire nut. Anything wrong with this wiring. Need help.

Red, is there a second switch somewhere?

Yes. Next to that timer switch is a second switch. This switch turns on lights in the garage while the old single pole switch was replaced with a intermatic switch that worked fine till I decided to replace it with a programmable switch that could use CFL bulbs. Old intermatic did not work with CFL.

How many wires from cables entering this box are there?