After you send a fax, it will be delivered in about 5-10 minutes. You can expect the status to then be updated in Salesforce about 2-5 minutes after it is delivered. When we receive a fax, it takes about 5 minutes to reach your org.
Certain factors can affect timing and speed. If there was a connection issue with the receiving fax line, we have a retry process which will extend the amount of time it takes to send the fax. The number of pages in a fax also affects sending speed, as more pages will take longer to send.