In the Universal Syriac Orthodox Church tradition about dormition and the associated fasting begins on August 1 and ends on August 15, with the feast of Dormition of St. Mary.
Fasting period is relaxed to 5 days, in Malankara (India) too, starting from August 10, and ends on August 15, by the Holy Synod lead by H.H Patriarch Aphrem and was addressed again by H.H Patriarch Zakka in the 80s.
Church of the East’s custom of fasting is dawn to dusk. It may have been also followed by the Madenhoyo - the Syriac Orthodox Christians in the Persian Empire, who had many traditions different from the Western Syriac Orthodox. The Western style is to fast until noon which is/was followed in Malankara (India) also. That is not to say that there is any prohibition of fasting till dusk.
My grand mother and mother both fast dawn to dusk especially during the fasting of dormition. Me too tried few years back to follow them, but failed to continue it latter.