In our state in India, some of scholars in the mosques are trying to keep the accuracy of the Azan timing by calling the Azan 5 minutes earlier for Subh and 5 minutes later for Magrib. They are keeping some minutes delay for other Azan also. At the time of Ramadan, they will trying to keep more accuracy by delaying to start the Azan up to 7 minutes. Is there any evidence in the Hadith to make the delay on the account of accuracy?
Changing the accurate time of Azan doesn't improve accuracy.
I think we can personally stop eating a couple of minutes before Azan of Subh, or start eating a couple of minutes after Azan of Magrib to be sure. But it looks weird that a mosque changes the time intentionally.
Also it is not accepted to perform Salat before the time of Azan. And calling the Azan earlier can lead to that.
Do your research in Bukhari. It is Sunnah to start the fast as late as possible and finish it as the prescribed time not later than necessary. The prophet forbid going to extremes and making our Deen difficult. The sub- Continent in notorious for this.