There seem to be two terms used to mean "twilight".
The Torah uses the term בן הערבים as in the time for the Mincha and Pesach offerings.
Talmudic literature uses the term בן השמשות
I know that there are differences in the length of twilight itself, halachically, as there are different opinions of tzet (when the stars appear.) However, I have generally understood that the time span of Ben Hashmashot is from when the sun begins to set (i.e. the "lowest" part of the sun is on the edge of the horizon) until tzet.
As בן הערבים is written in the Torah, it is obviously a much "older" term. I am assuming that there was no dispute as to exactly what that length of time was as there was an agreed / standard definition of when sunset begins and when tzet begins.
The Talmud brings in a debate of these two endpoints, which makes me assume that the definition of בן השמשות is not as clear.
My question is, do the Torah term and the Talmudic term refer to the same time span and these two terms are simply synonymous? Or are these referring to different time spans? If so, what are the differences?