How long should it take an angel to travel from Be'er Sheva to Sodom? Well, since you're immune to the laws of physics, it really should take no time at all. Yet, we find that while the three angels seem to take their leave of Avraham sometime during the day (they started eating during "the heat of the day"), וַיָּבֹאוּ שְׁנֵי הַמַּלְאָכִים סְדֹמָה, בָּעֶרֶב - "the two angels came to Sodom in the evening. (19:1) What took so long?
Rashi explains that the angels intentionally wait to arrive in Sodom in order to give Avraham a chance to argue with God and save the city. Only when Avraham's appeal fails do the angels proceed to fulfill their fateful mission. The Netziv (Rabbi Naftali Zvi Yehuda Berlin, Lithuania, 1818-1890) writes in his commentary to the Torah called Ha'amek Davar, that while the angels themselves can travel instantaneously, Avraham accompanies them a distance of three parsaot -- a considerable way. Only when they take their leave of him can they "transport" to Sodom. They arrive in Sodom so late in the day due to Avraham's insistence on considering them his guests long after they leave his home.
In fact, Rambam (Laws of Mourning 14:2) explains that the rabbis decreed that accompanying guests out of one's home to be a rabbinic commandment based on Avraham's behavior. Rambam writes, "The reward for accompanying [a guest] is greater than all [other reward]. And this is the law that Avraham established and the custom of kindness that he practiced: he fed travelers and gave them drink and accompanied them...and accompanying them on their way is greater than welcoming them...Even if one only accompanied his friend four amot, his reward is great indeed!"