When weather forecasts are given as high today of 25 and low of 10 is this for the time period of midnight to the following midnight or from sunrise to sunrise or what other method?

That will depend on what else the weatherman says; normally, it'll be clear in context. But generally, they are talking about sunrise to sunrise.

If the weatherman on TV at 10PM says "The high today WAS 25, and the low tonight WILL BE 10", then he's reporting the actual high temperature, and his forecast for the low in the next 12 hours. Please note that the lowest temperatures sometimes come shortly after sunrise; overnight fog can insulate the ground from the worst of the cold, but the first rays of dawn can burn off the fog and allow the temperature to go down a bit more.