When two prepositional phrases come at the beginning of a sentence, without regard to how long or short each is, there is usually a comma after the second one.
...At the beginning of the night, we were...
...After all of that, we were...
...Before dark on the 19th, we were...
...On Saturday after lunch, we were...
In each of these examples, the second prepositional phrase modifies the object of the first preposition: Of the night modifies beginning, et cetera.
And when these types of prepositional phrases -- that is, those that are just modifiers and not parentheticals -- come after the word and or but or so, there is no comma after those words before the prepositional phrases.
...So at the beginning of the night, we were...
...And before dark on the 19th, we were...
...But on Saturday after lunch, we were...
However, you have a different situation when the second prepositional phrase modifies into the sentence; then you have to put a comma after the first one.
...Between you and me, on Friday he is going to...
Happy punctuating!
Margie