Can I just say I am a big discover test fan, Never let me down. However if you have a faint 2nd line appear it could mean you are as I think the hormone in your urine has to be there for it to show up. I have used the test twice with the faint 2nd line and have been pregnant both times. As for the line showing up later than 20mins this could be a fault of the product. Have a look at the packaging for the companys phone number/website and question them. Also you could wait 3-5 days and test again with a good brand test.
Goodluck