I see following contradicting statements,

An application that uses the multi_socket API SHOULD NOT use this function, but SHOULD instead use curl_multi_setopt and its CURLMOPT_TIMERFUNCTION option for proper and desired behavior.

Call curl_multi_timeout, then wait for action on the sockets. You figure out which sockets to wait for by calling curl_multi_fdset or by a previous call to curl_multi_socket.

So first statement tells application that is using multi_socket should avoid curl_multi_timeout, but second statement speaks about previous call to curl_multi_socket()