That is largely at your discretion. I would not do more than one attempt at 23 and 25, we've had such great results with one attempt (much better than anything with frequency)
Not sure if you saw this but may help
http://genderdreaming.com/forum/gend...pink-blue.html
http://genderdreaming.com/forum/gend...frequency.html
http://genderdreaming.com/forum/gend...pink-blue.html