I’m guessing you don’t live where it snows. As Xema said, it depends on the kind of snow, as well as if there’s a sheet of ice over the top of it. That glaze will make it take longer, it’ll reflect the sun and sheer the rain off.
Of course the temperature makes a difference. If it’s 33 out, it’s really not going to melt. It’s got to be, I dunno, 37ish, before the snow starts getting melty, 40ish is about when you start seeing water running off into the road.
If it’s raining, like really raining out, that’ll get rid of a lot of snow really fast. In fact the first really big rain in spring, if there’s still a lot of snow out (more than a foot), seems to be the day that the sewage department dreads since they get all the water from the rain PLUS all the snow from winter all at once and end up with problems.
As for the surface, yes, that makes a difference as well. The grass will go last, the concrete and asphalt will melt faster. I’d guess that asphalt would melt snow faster than concrete since I think it holds heat better, but it’s hard to say since I don’t usually see them side by side in place I can easily compare them.
Lastly, yes, the sun pounding down on the snow will melt it faster as well. This is most noticeable near buildings/houses. The area closest to them where the sun never really hits might have snow for weeks longer than the area out near the street or on the other side of the house if it never gets warm enough to melt it w/o the sun.