There's a reason why the instructions in the kit tell you to check the result immediately after the waiting window is over. As long as the urine doesn't dry up on the stick, you'll see the accurate result.  As soon as the urine dries on the kit, the line will lose color and become discolored or grey, making you think it's an evaporation line. Doesn't matter if the line was bright pink or faint pink earlier. As soon as the urine dries, you can't tell an accurate result.