Ovulation test help!

When is the best time to start testing with my opk? SO and I have been trying for the past few months, but due to his new job our schedules are off and we haven't been able to try at the right times. So I'm hoping this opk will help us find the right time for a better chance. So! When is the best time to start testing for it, and has anyone noticed sooner conception while using them?