Driving a car in Greece is not easy! You have to be extra careful because the roads are small and narrow and local drivers drive fast as they are used to these conditions. Also there are a lot of motorcycles so you have to keep your eyes open from all the sides by checking all your mirrors regularly. Traffic inside the city is high, especially when the city shops are open. Taking the car inside the city in not wise and you will also have trouble parking your car and even risking to get a ticket. If you deside to rent a car I suggest to do so ONLY if you are willing to travel outside the city. Inside the city you do not need the car.
Driving from Heraklion is about 2:30 hours following the highway with moderate driving and speed. You do not need any GPS it is very easy just drive until you see the signs of Chania. Alternately you can make a stop at Rethimnon to see the city which looks a little bit like Chania and continue your journey afterwards. You have to be careful because there is no crash barrier in the middle and on some points there are Police speed radars. Avoid overtaking other vehicles because the road is very dangerous. As you drive you will notice many miniature churches scattered in different sides of the road; these small monuments have been placed from families/friends for someone that has had a fatal accident on that spot.