I want to start to build muscle on my arms?

i have only started using dumbbells i got 1.5 kg dumbbells from argos if i Curl 20 every four hours a day one at 9am then at 1pm then at 5pm then at 9pm then at 1am how long should it take to notice im starting to build muscle on my arms at the moment im fat im 34 waist and im 5ft 4