Easy to look up! By current estimates Earth cooled enough to have liquid water about 4.46B years ago and the first RNA emerged around 4.35B years ago. So it took just over 100 million years for simple forms of life to emerge.
Ok, so you are setting the scale as "from the present conversation back to formation of Earth" and saying that this is large in comparison to "from formation of Earth to formation of RNA". However, I respectfully don't see how this scale has any bearing on the probability of life forming around another system. Formation of life is certainly a prerequisite to the formation of intelligent life (the two events in question). Both could have a probability of occurring much smaller than 10^-24 (approximate # of finite stars in observable universe).
