Going from Goethe C1 to Goethe C2 for ETHz in 4 months

Question

I am currently studying German because I would like to study my bachelor's degree at ETH Zürich. To be admitted I need to either get at least an 80% grade in all Goethe C1 modules or at least a 60% grade in all Goethe C2 modules (I only need to pass the exam). I'm currently at a C1 level (but I don't have a certificate to prove it) and I've got approximately 4 months to prepare for the C2 level (2 months for the C1).

In my opinion trying to get at least an 80% mark in all 4 modules is too high a risk (I still make grammar mistakes - I've only been studying German for 3 years) and that's why I'm considering taking the Goethe C2. I would be extremely disappointed if I had to repeat the exams (they are extremely expensive and I've only got one year left before doing my bachelor's). From your own experience, is something like this feasible? Which learning resources could particularly benefit someone in my situation (ignoring the fact you don't know my own strengths and weaknesses)? And to make matters worse, I've only got 1-2 hours daily to spare.

I'm pretty new to this forum so I hope I'm not breaking any rules on what you can ask :)

EDIT:
Source: Sprachanforderungen (ETH Zürich)

Answer 1

If you really are at level C1 [1], you should go for the C1 exam. This is because moving from C1 to C2 is arguably the biggest step between two consecutive CEFR levels.

In an answer to the question How long between each CEFR level for learning Spanish? I described the cumulative effort to reach the CEFR levels for Spanish based on the curriculum in a language school that takes those levels very seriously. According to the brochure they made available a number of years ago, you needed two years with 120 classroom hours each (plus some learning at home, obviously) to move from B2 to C1. Extrapolating from that, moving from C1 to C2 requires at least another two years, not four months. You may be able to cut the time in half by living in a German-speaking country (which, in my own experience, is easy enough at level C1), but not reduce it to just four months.

If you have just one or two hours per day that you can dedicate to language learning, I strongly recommend that you use them to prepare for the C1 exam, not the C2 exam.

(Background: I am a native speaker of Dutch who studied English and German at university and has lived in Germany for just over 10 years. I have also helped a few Chinese students prepare for the TestDaF exam, which is roughly at level C1. I have no experience with the Goethe Institute's exams for levels C1 and C2.)

[1] For clarity's sake, a general C1 course is a course that helps you reach level C1, not for learners who have already reached that level. An exam preparation course for the Goethe Institute's C1 exam is for learners who are at level C1 but want to prepare specifically for the exam format.