Faint line in opk

Today is the first day I got a faint line in my opk. I know it is not a positive until it matches the control but I was just wondering if anyone else has experience with the opk lines fading in or out in regards to your ovulation. Will this line get darker as it gets closer? I also read you ovulate about 48 hours after a positive.... When I plug in the positive on glow it does not make it seem that way. Any suggestions?