If i have a location and the wan service is offline, the meraki switche will not have a connection to the Cloud anymore. Is there something like a timer, when the switches dont't work (local switching without wan Service) any more?
I don't think the switch will stop working before the license runs out. I'd guess that on each change the switch would download its new expiration date. If the WAN connection goes down I'd wager to guess it'll continue working at least up until that date + 30 days (grace period). I'm not sure whether the switches would stop working on their own without being instructed to do so manually by a Meraki employee. This sounds like quite a hypothetical case anyway, Meraki really isn't meant for offline uses. What is your use case?
There are some config changes you can do (layer2) from the local status page, which would mean that you could use it offline (if the license is not kept locally). However, I would not risk using the switch this way.