how to implement accurate milisecond function

[VIKS]

I am new to nrf51822. I am trying to convert my Arduino code into NRF51822

I need something like this

currentMillis = micros(); //microseconds since the Arduino board began running if(currentMillis-past_time>=1000) { do something }

What is the best way to do this in NRF51822? Should I use RTC or go with simple timer? Can anyone share their function if they have already implemented?

Thanks