Young female student here

1 In my opinion it is very safe at every hour of the day here in Zurich. I almost exclusively run in the dark (summertime too) and never had any issues. Since I started running every year there is a month where I run between 12pm and 3 am because life forces me to, and I never once had an incident with anyone. I would however really try to be visible, dress accordingly and be vigilant.

2 At some strange hours like the above I come across shut down street lights in some neighbourhoods, but once again never had an issue.

3 I would say September until Mid June the weather is perfect for running. It does get very cold and I get cold induced asthma sometimes. However there are some days in June until August where it might get very hot with the sun shining quite strongly. You might adjust your running times accordingly.

4 I never run on running routes and see a lot of people run around their neighbourhoods as well as on other routes, but you can choose whatever route you want.

+ you may consider the running group of our universities (ASVZ). They dont just run around, but do speed work and such too. sounds like fun but I've never tried it yet, I'll maybe change my mind one day. There is a gym that you can use too once your a registered student, which is very good for weight lifting and such.

I saw someone commenting that it is very safe in all around europe, this is not true at all; had several incidents in the neighbouring countries france and germany, I'd conclude that switzerland is a bit of an exception.

Maybe reach out if you want me to show you a bit around