Do come and explore the Causeway Coastal Route! It is well worth it, especially when you have made it to Belfast.
I would encourage you to get up and on the road earlier rather than later in the morning. This will give you more time to stop and take in the beauty of the drive, get a coffee or ice cream en route, explore a village like Glenarm or Cushendun, eat fish and chips in Ballycastle…
Head out along the shore of Belfast Lough towards Carrickfergus and basically follow the road around the coast. Here is a map which you may find useful, as well as places of interest along the way. http://www.visitcausewaycoastandglens.com/Portals/0/downloads/CCRMap2018.pdf
I would encourage you to buy your entrance ticket for the Giant’s Causeway online in advance; it is also cheaper to do this. You will also need a ticket to cross Carrick-a-Rede Rope Bridge. Even if you have to wait a little before your allocated time comes to cross the Bridge, you can explore Larrybane and Ballintoy Harbour, both locations used in the filming of Game of Thrones.
After exploring the amazing hexagonal stones and columns of the Giant’s Causeway, you can assess how much time and energy you have left. You may visit the whiskey distillery in Bushmills or decide to stop off at Dunluce Castle. Or head for the seaside town of Portrush, with its restaurants around the harbour, or to Portstewart to watch the sun set into the sea, before heading up to Coleraine and returning to Belfast on the main A26 and M2.
Go for it! It will be a day to remember. Maybe you will find yourself wanting to return and stay for longer in this stunningly beautiful part of Ireland!
I wish you a pleasant trip.