Hi Tiger, You would say, "I will graduate [later]." Since you have taken a year off, your graduation will be pushed back (e.g. from 2018 to 2019 (later - further in the future)). "slow" has the meaning of speed or how fast things can done, but "later" has a meaning of a time after a time you have mentioned. "will graduate" is needed as you are using simple future tense to describe something that will take place in the future. Example: " I have taken a week off. I will complete my project slowly." (focus is on the fact that you are taking your time to do it though there is still a meaning of a future completion with "will complete") "I have taken a week off. I will complete my project later." (focus is on the fact that you will complete it at a time further in the future, without any mention of speed.)

fast/slow = speed of doing something early/late = time so 'late', or 'a year late' is good. :)

i'll graduate a year late