The Banffshire Journal of 10th June 1897 announces that William Clark has opened a new studio in Low Street. However, it does not say he closed his old premises in Baron Street. He may have had two branches.
Further investigation shows that he started business in Buckie about 1878 and his original premises were in Baron Street. They were altered and extended in May 1883. The Baron Street studio closed when he moved to Low Street in 1897. The Low Street premises were earmarked as the site of a new bowling green and in an advertisement dated from Low Street on 15th May 1901, he announced his intention to move to new premises in Baron "Lane". By July 1901 he is announcing that he has removed to his new premises in Baron "Street". When he died in 1909, the business was continued by two of his daughters, with the assistance of a brother, who had a photographer's business in Huntly.
In conclusion, any picture you have with the address Low Street was taken between June 1897 and May 1901. Photographs with a Baron Street address may be before or after these dates and you will have to rely on things like costume to pinpoint when they were taken.