Mahayana - Advaita - Theravada realisations

Mahayana claims that the realisation of Nirvana in Theravada is dual while Mahayana is non dual. I have read that Advaita (the universal consciousness theory) is the same as Mahayana. - Does that mean that Mahayana claims that the universe is unreal, and that Everything is consciousness -- which means that the universe (and the time and space existing in it) is illusory, and exists only from the Point of view of the separate self but not in reality? - Or are they not as extreme as Advaita, but instead only claims that time do not exist (except) in our minds -- but Everything is consciousness -- or is there difference between Mahayana and Advaita Vedanta? I want to learn both paths and then use both for my benefit. From what I have read the realisations are not the same and I would really like to understand the both realisations. Thank you for your patience and your energy