How long between your death and the enemy getting killed, can you still get an assist?

I feel like this happens a lot. You get dove under tower bot lane as the ADC, get few basics and maybe an ability off and die, but then your support goes complete Rambo and chases down the enemy for a return kill, but sadly no assist for you, even though you did damage them. I feel like if I was alive I would have gotten that assist. I know execute timer is 10 seconds or so from death and last enemy damage taken. But it seems there is a lot less time for earning that after death assist.

Note, this is implying that you actually helped out with the kill for the assist, not just you were around and not doing shit while some enemy died in your vicinity.