I have heard that the GPS system is more accurate, and less accurate on some specific hours on the day.

If this is true, how can I get the information on when GPS is more or less accurate at my location? And how big is the difference?

I guess this depends on where in the world you are, I'm living very north, so it's maybe has a bigger effect here. I also think it has to do with how many GPS satellites you get signals from at the moment.