It would make far more sense for you to choose one thing to use at the end if you're actually suggesting that someone spend the same length of time studying English as doing the other thing.
You need to spend the same amount of time practising English each week as you do watching TV.
This kind of structure is sometimes used in a more negative way, such as (parent to child) "If you spent as much time practising English as you do watching TV, you'd have far more chance of passing your English exam!"