I have a test here and it says not to read the window after 10 minutes. What happens after the 10 mins???

I took it very early this morning and could only see one line... they have a pink background and purple lines. I felt crappy so went back to bed with DS and now 2 hours later i can see a faint 2nd line. What does this mean??? i think i can see the faint second line because the test window bit isn't pink anymore but now offwhite so it seems to have made it visible.

Taken a second one now and only 1 line