hi, im using guiminer and the speed is 130
can it hurt my graphic card if i mine at night?
Not at all if your temps are good. There's no difference between mining during the day and at night (besides from temps), and when you are on or off (changes only the load and the mhash depending on how much you use the graphics). If you're not overvolting (excessively) and your temps are good, and your PSU can support the load, it's perfectly fine