opk question

Andrea
Ok so I've been trying to conceive #3 for about 8 months now and I've never used opks before and decided to give them a try. I just got them today and am wondering do I use them once or twice a day? what times or does it matter?  
my first dd was a pleasant surprise and my ds took us about 4 yrs conceive, (2 yrs ntnp and 2 yrs ttc). I am almost 35 and my husband just turned 47 so I don't really want to wait, so I figured I would do everything I can to help pinpoint ovulation, especially since I have very irregular cycles so I'm charting my temps also and bding a lot. any advice would be appreciated!!!