Rapid respwns are each 2 months , Cipsoft altern between double exp and rapid respwn , for example this month is Rapid respwn , and then in November will be Double exp weekend , and then in December again rapid respwn.
In addition of that you can check the schedule of tibia events to ser the exact date of this events.
https://www.tibia.com/news/?subtopic=eventcalendar