Ronald from the Google Merchant Center team posted a thread at the Google Merchant Help forum saying that scheduled uploads currently do not work, instead upload your files manually. Of course, to many merchant, manual uploads is simply not an option. So hopefully this will be fixed soon.
We are currently experiencing an issue with the scheduled uploads feature in the Google Merchant Center. Our engineers are aware of this issue and working to resolve it. In the meantime, please upload your data feeds manually. We will update this thread once this issue is resolved.
So if you don't see your product feeds being updated on Google Product Search, this may be why.
Forum discussion at Google Merchant Help.