In my GAE app I am serving static content as follows (those are my entries in my app.yaml file):
handlers:
- url: /c
GAE should work fine with 10m
value.
Most probably that was because you were signed in with your google admin account.
GAE returns no-cache
for such accounts.
Trying opening the same page in an incognito returns proper cache expiry times.
By default GAE sets cache to 10 minutes, so even if you didn't set any expiry - you should see 10 minutes instead of no-cache.