Let me also first congratulate you for qualifying to the World Championship! I also very much applaud the courage to ask about the details of the international competition -- that is exactly what this forum is for! The rules have a section dedicated to the international competition but it is obvious that it does not explain everything clearly enough, so let me try to answer your questions in a bit more detail.
As @adrianmatejov mentioned in his reply, the Junior competition starts with a so called "Setup day". Last year the organization committee (OC) has tried to make sure all interviews happened on this day, so that the following days could be focused on the matches. The technical challenges are a new addition -- last year they took place during the last competition day and I think it will be very similar this year.
You do not need to worry about the details (as in "what time do the interviews start" or "when does our interview start") -- the exact timetable will be published before the competition.
Once again, thank you for your questions and please do not hesitate to ask more of them if we haven't covered everything.
Best of luck!