BFP or evaporation line?

Hi guys! So i took this test this morning and after the three minute count time, it appeared negative but fifteen minutes later i check again and there was this line. Positive or evaporation line? This keeps happening with the tests i take. They’re negative within the amount of time you’re suppose to watch but positive like this (some were darker than others) between 5-30 minutes after i had taken the test. Thoughts??