Just today, I did a booking with UA miles. SNA - ORD - FRA -ARN. Return is CDG - FRA - DEN - SNA.

It took about 15 minutes for UA to book and hold all flights. Key was that I knew which flights I wanted and just read them off to the agent. I also was aware, from the ANA site, that the flights were available (except for the potential of Starnet blocking).

So bottom line is that it can take an hour or so, or it can take minutes. A lot of it depends on how prepared YOU are.