Hebrew meaning of “between evenings”

I’m trying to understand a phrase in Exodus 29:39 and Numbers 28:4. The phrase is "בין הערבים."

This seems to literally mean "between evenings." It is present here in the language of sacrificing two lambs daily. One is clearly "in the morning" or in Hebrew, "בבקר." If the author means "in the evening" then why is this not just בערב? Is there something to this phrase that idiomatically means "evening?" Why the distinction?

Could this have to do with the fact that evening spans the boundaries of two days while morning is in the middle of one day?

Septuagint has "το δειλινόν" in Exodus and "το προς εσπέραν" in Numbers. These don’t seem to carry the same ambiguity as "between evenings." They seem to just say "at dusk" or "towards dusk"..