Background sync at specific time Interval.

In one of my requirement,I have to scan BLE device ,connect and get some data at specific time interval (e.g. at every 3 hours) in background.

I have to sync BLE Device data in the background without any user interaction at specific time interval. (e.g. 8am,11am,…so on…)
I have spent a lot of time but i am not getting a proper way for this:
I have tried following approaches for this:
Background-Fetch: I am not able to get callback at specific time period.
Local Notification: I am not able to get callback without user interaction. I am getting callback only in foreground.

What are the possibility to fulfill our requirement for syncing in background at specific scheduling time period?
Please provide appropriate suggestion.

Thanking you very much!