CURLINFO_STARTTRANSFER_TIME man page
CURLINFO_STARTTRANSFER_TIME — get the time until the first byte is received
CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_STARTTRANSFER_TIME, double *timep);
Pass a pointer to a double to receive the time, in seconds, it took from the start until the first byte is received by libcurl. This includes CURLINFO_PRETRANSFER_TIME(3) and also the time the server needs to calculate the result.
See also the TIMES overview in the curl_easy_getinfo(3) man page.
Added in 7.9.2
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.