to add bit more in continuation to Xulfiqar's byline .
ensure that you have enough fuel supply when crossing border. There is enough respectable border rest places in 1km radius on iranian side.
Enter into Pakistan at day break complete formalities and arrive Quetta & STOP. goto Bus terminal and check what time buses leave in direction of your destination,
since your location is in UK, I assume you will be heading for a town in Punjab or in Azad Kashmir. Leave 30 minutes ahead of buses and exercise caution across, Foreign plate vehicles are soft targets,