The herpstat 1 will keep the temperature at the set temperature. personally I would set it to 90 degrees as this gives some room for error in both directions.
In what way do you want to simulate the day/night? as in temperature drop (which is unnecessary and not recommended) or light/dark? (which is not possible without reducing heat. I would recommend that you ditch the white light and get one of these: http://www.petsmart.com/product/inde...uctId=11147193)