Religious practices vary from time to time and from region to region.
Time zones vary across the world. It is Sunday early morning in America now and probably Saturday evening in Trinidad. All these places will celebrate the same festival at different times. Do you think this is wrong? These are based on the region, and time.
Likewise, some celebrate Hanuman Jayanthi on the day Hanuman took birth, few others observe Hanumad Jayanti as the day Hanuman flew to catch Lord Surya, in some other regions the day Hanuman had darshan of Lord Rama is celebrated as Hanumad Jayanti. There are many others, who also celebrate Hanuman Jayanthi on the day Hanuman had Sita Mata darshan in Lanka. It is also celebrated on the day Rama returned to Ayodhya after being coroneted as the King. There are still many more who observe Hanuman Jayanthi on the day Hanuman went to Gandhamadhana Parvata (mountain).
So, different regions celebrate it on different days. There is nothing wrong in this.
In Ashrama, we celebrate all occasions of Hanuman Jayanthi.
(Q&A Session 16 Apr 2017)