This knowledge article explains the difference between "Processing Time" and "Transfer Time" as reported by monitors
What is the definition of "Processing Time" and "Transfer Time" for a monitor?
Monitors hosted by App Synthetic Monitor
After the HTTP request is sent, the monitor waits for the very first bytes of the result. That period is defined as "Processing time". Afterwards, the time taken to complete the remainder of the HTTP response data is called "Transfer time".
Release: APMCMB99000-8.3-App Synthetic Monitor-Basic Option