Great question with multiple answers based on conditions. So let’s explain how long the wait time is.
When you have never created a feed before and you have for the first time added a feed to Google Merchant Center, then the approval process takes between 3 to 5 business days (weekends don’t count).
Make sure that you do not have any feed errors by checking Products > Feeds > Click on your feed > Processing. Also check that your products are not missing any crucial requirements by checking Products > Diagnostics
When you have an existing feed connected to Google Merchant Center and have all previous products already approved, then it takes around half an hour for it to reflect in the account.
You can check the processing of the feed info in Google Merchant Center by going to Products > Feeds > Click on your feed > Processing
And after half an hour, the info will be updated and can be viewed by going to Products > All products
The info will also be reflected in Google Ads, however this can take up to 24 hours.