If you are using a wooden spoon, plan to be at it a while...
Or you could take the easy option and use an electric mixer. If you do mix, it is likely that after a few minutes the ingredients will have formed into hundreds of tiny lumps. Keep on mixing!
When the mixture comes together in one lump and starts to stall the mixer, it is ready. This happens when the sugar is broken down. If you used caster sugar, it should happen fairly quickly (within five minutes). If you use regular sugar, it will take a little bit longer.