Complex sentence: Ali Astamirov worked for a privately owned radio station in Grozny, then he worked from 1998 to Oct.1,1999 for the Chechen branch of the then-independent Russian television station NTV (Russia).
Split into simpler sentences: Ali Astamirov worked for a privately owned radio station in Grozny. From 1998 to 1 October 1999, he worked for the Chechen branch of the then-independent Russian television station NTV (Russia).