Asslam o alikum

Recently, I have got government job as a PST teacher. I have taken two attempts of CSS exam and upcoming would be last one. I am pretty confident that insha'allah Allah will bless me in this year. But I want to take my last attempt, if I skip next attempt, I think my age would be over age for CSS-2016 but I can attempt CSS-2015 withing age though. I have also qualified ASI Police test, however, I am one step away to get this job also. Nevertheless, my question is that, how many years I need to continue my government job to avail through proper channel. I have heard that we need two years service of govt job to avail through proper channel for CSS. However, I am alhamdulillah well prepared for CSS-2015 but if I join ASI Police training that is one year, might be I won't be able to take my attempt of CSS-2015 with that strength and enthusiasm. Now I am coming to the point, what is the rule of 'through proper channel'?. Having done one year govt. job, can I avail through proper channel? Some times, I am thinking that I should take my third attempt/CSS-2015 since I am well prepared and every thing goes to the level of perfection. I am in need of sincere suggestion.

Thanks in anticipation
Exclusively