How long you wait depends on the severity of the leak. Real bad leaks usually result in pretty obvious symptoms and observations that are easy to diagnose. It's the slower leaks, including those where the leakage dries up and evaporates before you get to see it where this dye is the most useful.
If it takes, lets say, a thousand miles for you to lose a quart of coolant, you may need to drive 50 to 100 miles to have enough time for the dye to work its way to where it can be seen. If you lose a quart of coolant in a day, perhaps 50 miles of driving or less, you can probably drive just five miles, then check for the yellow stain. If you can't find any indication after a hundred miles, just keep checking at regular intervals until it shows up.
Auto parts stores will have the dye for the fluid you're leak-checking, and those that rent or borrow tools should have the black light.
Thursday, April 2nd, 2015 AT 6:44 PM