The priority registration opens on April 24th at 21 CET. The open registration opens on May 1st at 21 CET.
All important info can be found here at IDF page.
Remmber, the first round of registration is the priority one, that means for the riders till the 30th place in the ranking. Rest of riders can register on May 1st.
You can't registrate without IDF membership and havIng paid the IDF membership fee. For succesfull registration for Kozakov Challenge 2016 you have to pay the admission (step of the registration process) for the number of cathegories you want to race in and choose if you want to take the Tuesday freeride. When you're succesfully registred your name is shown in the list on this page.