While the feed will always be updated in real-time*, Facebook only fetches the feed periodically (by default once every 24h).
So while the feed is always up-to-date the changes still take time to end up in your FB catalog. You can trigger a refetch manually from your feed settings page in facebook business manager.
* What does real-time mean?
Most feeds with less than 10000 products generate in a matter of seconds or minutes. A short while after you hit the "Save Settings & Generate Feed" button in your Flexify Admin your feed should be up-to-date. However, it may take a while for Facebook to come & fetch the products in your feed.
If you are on one of our custom plans with >5000 products, feed generation may take a little longer to generate. Flexify can generate large feeds with hundreds of thousands of products but it requires a more hands-on approach to mitigate the timing issues. To summarize: if you need more products, we are happy to help you, just get in touch!