Google most frequent automatic feed update is once per day. However it allows feeds to be "re-fetched". Re-fetching can be manual in GMC, or triggered via API.
After each time the app finishes a feed run, it triggers the re-fetch via API. Please note that this only happens to "connected" feeds, i.e. feeds that have a Merchant Center connected.
The re-fetching, either manually in GMC or automatically by the app should reflect in the upload time updated in GMC.
