How to enter low power mode or sleep and wake up, also how to keep the rtc active.

[RitD]

In my application, I want to implement low power modes and also perform certain tasks like updating the characteristics based on application timers and also update the local time in a global variable updated by the rtc.

Please guide me about how to go about entering, waking up from low power mode and sleep and performing all the tasks as well.

[Kenneth]

I believe most BLE peripheral example include app_timer library, and you can create and start app_timers that run single shot or repeated. In the app_timer timeout handler you can run code as you wish. Please see this blog post description on how to include app_timer:
https://devzone.nordicsemi.com/nordic/short-range-guides/b/software-development-kit/posts/application-timer-tutorial