Positive OPK but im confused

Victoria • http://FertilityFriend.com/home/5cafdb

Can i have sex 8 hours after i get the Clear Blue smiley face? or do i have to do it right when i get the smiley face.? i had to work late so i couldnt until 8 hours later.

August 26th

830am -opk

315pm +opk (was at work)

1030pm -opk (right b4 having sex)

Do i even have a chance. Why did it turn negative that same day.?