Seems like unusual format of shakedown will be used, as beginning is for P2-P4:

12.4.3. Shakedown
Shakedown will take place on Thursday 20 April at SD Okić as follows:
• P2, P3 & P4 09:00 - 10:45
• P1 & invited P2 drivers 11:01 - 13:00 (first run according to start list)
• All drivers 13:01 - 15:00