A little but you never get back as much time as you lose going uphill. It's the same as in a headwind/tailwind situation. You spend far more time going slower than you spend going faster, so you don't have enough time to make it up.

To illustrate an example, if you climb up an 8% grade at 4mph for an hour you would go 4 miles. Using the calculator here, if you turned around and went back down that 8% grade and put out the same power you would go 37.2 mph, or 45mph in the drops. At 45mph, that 4 miles would take 5 minutes and 20 seconds. So the 8 miles total would take 1 hour, 5 minutes, and 20 seconds, at an average speed of 7.35mph. If you use the calculator and remove the grade, the same rider could have done the 8 miles in 29 minutes and 49 seconds, or 26 minutes and 31 seconds in the drops.