What the heck does this mean?

Ta

times:

5/17-5:30 am-negative

5-17-10:30 pm-negative

5/18-1:30 pm negative

5/18-10:30 pm- getting darker..

5/19-11 am- darker still

5/19- 4:30 pm, darkest

5/19-8:30 pm ??

5/20-11 am-negative

5/20 - 3:15 pm negative