I did it after dinner, just before bed. So around 10pm.
I showed partial ferns for about 3days and then I showed a full fern once.
When I showed the partial ferns I then when I showed the full I again. I only had to DTD 3 times and it worked.

I had no idea what I looking for so don't stress if you don't see anything.
You will know when you see ferns, they are amazing.

How long are your cycles??

My cycles are normally 28 days so I started using MB at around CD15 and then I "o" around CD17-18. Hope this helps.