Time for getting an assist??

I play support alot (especially j4), and sometimes backoff a little early out of the fight because my HP is getting very low. then after 2 seconds, their adc (which I pushed all my CC and stuff on) dies, but I don't get an assist?? what is the time you need to make damage/cc to an enemy champion in order to get assists??? It kinda pisses me of that I bring their ADC so low but get no assist
Report as:
Offensive Spam Harassment Incorrect Board