The website data is constantly available for all feeds, the frequency that they are pulled from the website is down to the 3rd party application. This means that your latest stock and price changes will always be available.
Therefore prices and stock availability will be current at the time Google pulls the data, by the time Google has processed that feed then the stock / prices may be out of date. When Google then verifies the feed against the website it finds discrepancies between the two which may result in warnings within your merchant centre.
If you do have trouble with this scenario then try what Google suggests in this link: