Welcome to SD!
is that a 120 liter tank? its a little small for discus and only having 2 discus will cause problems b/c they are schooling fish. There are lots of stickies in the beginner section that will be helpful for you. Starting off with plants and young discus can be a challenge too but not impossible. would be easier to grow them up to adults first then add plants and substrate. and length of cycle is as long as it takes to complete its cycle. there are things available that can help speed the process. doing a fishless cycle is faster than with fish and no chance of a loss. there is also a product called pure aquarium that can cut the cycle time in half. good luck!