IMPORTANT: Due to a high volume of requests, it can take up to 10 business days for Google to complete a review of your site during Pending status. This is extremely rare, however, and most requests are processed within 72hrs.

Upon first submitting a product feed to Google Merchant Center, your feed will enter a state of Pending wherein Google crawls your feed, website, and also manually reviews your website for approval.

Pending typically lasts between 24-72 hours before Google will either Approve products, Disapprove products, or even Suspend your Merchant Center account based on their findings.

In the app, Pending is indicated by the Daily Stats being colored yellow:

The only thing you can do about this is wait for Google to complete its review.