Close BLE and go into sleep mode

Hi,
I am using DA14585 and SDK6.4.2.
Our customer designed a mode named "LOW POWER MODE"
Once finding the voltage is too low, DA14585 will close all functions (BLE, RF, peripheral...etc.) except the RTC.
It means the date & time should be kept in somewhere and close all functions until battery starts charging.

Following is my plan, I am not sure if it works or not. Could you please give me some suggestions?
1. Declare a "uint32_t seconds" to save the time in UNIX timestamp format and be sure that the variable is stored in "retention_mem_area0".
2.使用TIMER0或时间R2 to add 1 to the variable every second.
3. Stop BLE advertisement and go to extend sleep.
4. When the device is charging, wake up and start advertising.

By the way, I am just curious, Is there TIMER1 in DA14585? I can find TIMER0 and Timer2 but no TIMER1 in documents, why?

Thank you very much.