What is the unit of measure for timeTaken_d in Azure diagnostics?
It's in milliseconds, as per this document.
timeTaken: Length of time (in milliseconds) that it takes for a request to be processed and its response to be sent. This is calculated as the interval from the time when Application Gateway receives the first byte of an HTTP request to the time when the response send operation finishes. It's important to note that the Time-Taken field usually includes the time that the request and response packets are traveling over the network.