I have a RHT7500 series thermostat and when I install it and try to program it the incorrect date displays. Example, Today is Tuesday and it displays Friday as the current date. I was never given the option to set the date/year & time. Also the unit will not work even when turned on. Removed the battery and left it out for about five minutes but when replaced the day stays the same as previous setting.

Any suggestions?

Your install manual is here: http://customer.honeywell.com/techlit/pdf/69-0000s/69-1730.pdf

That thermostat requires a lot of setting up to do. See page 29 for time & date. It's not just connect the wires and go.