When Ross leaves Trenwith the sun is still setting; it was close to setting before he went. Then when is on the cliff top, in one shot the sun has just set and the next it is higher in the sky again.
Ross' beard has grown naturally and evenly across his scar, which wouldn't normally happen, showing it to be makeup.
When Ross saves Demelza and her dog in the town square there is an alarm box on the wall directly above them. This technology didn't exist during the 1700's.
Ross attends the wedding without shaving beforehand. Surely a gentleman would shave before putting on his white shirt and coat.