-- You could go for a walk 2 hours later after you finish your studies.
-- First, you have to finish your homework so that you can go for a walk two hours later.
-- If you could go for a walk 2 hours later, you could come with us.
-- (Repeat of first sentence)
-- I will give you the money you need in case you want to watch that film later.
('Could' isn't necessarily wrong, it's just not appropriate for the context. If there was something that would likely prevent you from seeing the movie, 'could' would make more sense. Though, if that were the case, I would use 'are able to'.)