This seems to indicate that the cave in which they had been camping was one day's journey from Jerusalem. That would answer the question of Machpelah at Hebron. A day's journey was 16-20 miles.
Crept into the city. Nephi left his brothers outside the city wall. He himself got into the city. Just how is not explained. In the large gates of a walled city, there was a small door or rather window, through which those who were entitled to enter might do so, when the gate was closed for the night. He might have literally "crept" in through such an aperture, by the grace of the watchman. It was always a small opening, sometimes only two feet square.
Nephi, the son of a prominent, well-to-do citizen, coming alone to the gate, a belated wanderer, unfortunately overtaken by the shadows of the night, might readily obtain an entrance through what some have called "the needle's eye," particularly if he had a piece of money with which to make his account of himself plausible; whereas, if the brothers had come together at that hour, suspicions might have been aroused. The wisdom that inspired Nephi is seen in his conduct, and his account is so simple, so natural, as to make a perfect impression of its authenticity on the mind of the careful reader.