To maintain active product data, you must update your data every:
A full feed should be submitted at least every 30 days. If your product data changes regularly, you may upload your full feed up to 4 times per day. For updates to your price and availability information in Merchant Center, you can use an online product inventory update feed as often as your price and availability data changes.
Read more here: https://support.google.com/merchants/answer/188477