Ramadan will probably start on August 20th when the crescent of the new moon appears and end on Sep. 18, IF the new moon is observed on that day.So it depends on the moon, the clouds, and the human eye.
During the month of Ramadan the suq is very busy and the traffic is quite hectic before sunset, because everybody must be back home and break the fast at sunset. At that time the streets are deserted (this is of course not the case in the Christian districts). Some (all?) mosques serve break-fast meals, which is an interesting sight.
In the feast after Ramadan, you will find the souq of Aleppo completely closed for some 2 or 3 days.