During the hot summer period, it is usual that on Fridays evening and Saturdays morning there is high traffic and usual a traffic jam on the road from Thessaloniki to Halkidiki that could be a nightmare for you. The same situation happens on the road back to Thessaloniki on Sundays evening.
Below you can find a live traffic map.
There are alternative roads that you can use in case of a traffic jam, so be sure to check this map before you drive.