Ok, so from what I have heard from most people, is that it is hard to prove to the authorities here that your foreign insurance is good enough. Plus, if there is a time when you need it, you usually pay upfront and get reimbursed by your insurance either. That increases the risk of them not paying for some things as well then.
What I did is just to get here. No need to worry about your insurance. Once here, go to www.comparis.ch
and find a plan. They are not that much. Mine was sfr200, that is sfr50 less than what my family allotted me. (Therefore letting me keep the extra.)
You have 3 months to sign up and prove it to the authorities. I would not wait more than a few weeks to get one though. And not to worry about accidents. Swiss law says that coverage backdates to the second to you step foot on Swiss soil. Your entry date.
Something to note, if you intend to leave the country, do not forget to get the abroad coverage. It's an option you must check or else you are not covered on many plans.