Q:

When a Google throttle daily limit has been reached, was the limit calculated from the last 24 hours or was it calculated since midnight?

We are trying to avoid hitting the Google throttle limits; so we would like to calculate our usage, and delay the requests when getting close to the throttle limit.
Is the daily limit calculated from midnight to midnight or is it calculated based on a rolling 24-hour period? If it's from midnight to midnight, then what timezone is being used? UTC?
Also, will the same apply to hourly limits, etc.?

A:

From How resources are replenished:

App Engine tracks your application's resource usage against system
  quotas. App Engine resets all resource measurements at the beginning
  of each calendar day (except for Stored Data, which always represents
  the amount of datastore storage in use). When free applications reach
  their quota for a resource, they cannot use that resource until the
  quota is replenished. Paid apps can exceed the free quota until their
  spending limit is exhausted.
Daily quotas are replenished daily at midnight Pacific time.
  Per-minute quotas are refreshed every 60 seconds.

You can also see in your App Engine Dashboard the current info specific for your app, like this:

