A.T. Robertson Commentary Acts 1:12

"Then returned they unto Jerusalem from the mount called Olivet, which is nigh unto Jerusalem, a Sabbath day`s journey off." — Acts 1:12 (ASV)

Olivet (Ελαιωνος). Genitive singular. Vulgate Olivetum. Made like αμπελων. Here only in the N.T., usually το ορος των Ελαιων (the Mount of Olives), though some MSS. have Olivet in Lu 19:29; 21:37. Josephus (Ant. VII. 9, 2) has it also and the papyri (Deissmann, Light from the Ancient East, p. 170).

A sabbath day's journey off (Σαββατου εχων οδον). Luke only says here that Olivet is a Sabbath day's journey from Jerusalem, not that Jesus was precisely that distance when he ascended. In the Gospel Luke (24:50) states that Jesus led them "over against" (εως προς) Bethany (about two miles or fifteen furlongs). The top of Olivet is six furlongs or three-of a mile. The Greek idiom here is "having a journey of a Sabbath" after "which is nigh unto Jerusalem" (ο εστιν εγγυς Ιερουσαλημ), note the periphrastic construction. Why Luke mentions this item for Gentile readers in this form is not known, unless it was in his Jewish source. See Ex 16:29; Numbers 35:5; Joshua 3:4. But it does not contradict what he says in Lu 24:50, where he does not say that Jesus led them all the way to Bethany.