Grass does grow some in the dark but for grass to really grow the grass needs lots of sunlight, water etc.
But even at night when the grass is not getting sun the grass is still growing.
Now if it were complete darkness all the time then the grass would not be able to grow or survive.
But as long as the Grass is getting some sun during the day then the grass will grow at night as well as during the day.
The amount that grass typically grows per day is around .06 inches to .20 inches per day.
The actual rate of growth for grass depends on the type of grass and the amount of water the grass gets as well as how much sun the grass gets.
On average though most grass grows at a rate of 2 to 6 inches per month.
cutting grass does make it grow faster and healthier than not cutting the grass.
When you cut the grass you cut off the tip of the grass that contains hormones that are released from the grass when help to make the grass grow faster, thicker and healthier.
So if you cut your grass before it gets too long then it will grow back faster, thicker and healthier.
That is as long as you do not cut the grass too short or scalp the grass.
Make sure your grass is cut to a good height and your lawn mower is not scalping the grass.
Also make sure your mower blade or mower blades are sharp and ready to cut the grass properly.
Dull mower blades may cut grass but it doesn't do a good job at cutting grass.