Capacitors tend to be lower precision than resistors. ±20% is not uncommon, and you sometimes even find ones with -20%, +80% tolerance — meaning that if it’s nominally 10 nF, it won’t be less than 8 nF, but it might be as high as 18 nF. Correspondingly, circuits usually aren’t designed to require capacitors to be very precise. If the instructions don’t say otherwise, a 20% capacitor will probably work fine. (In fact if you don’t have the right value cap but you do have one that’s within a factor of 2, there’s a good chance you can substitute it with little or no ill effect.)
