I'm doing a network analysis with ESRI's ArcMap 10.5. As part of this analysis I'm being asked to compare routes at different days and times to determine the impact of traffic congestion on routing. I'm curious, for a Route analysis if you leave the "Use Start Time" radio button unchecked under the "Analysis Settings" tab how does Network Analysis calculate travel time? Is it simply using free flow, i.e. posted speed limit, conditions? Is it using an average of travel times throughout the week? I know my network data set includes traffic information and I get different results when I pick different days and times. In fact, the results are exactly what you'd expect. If you pick rush hour travel time is worse than on the weekends. However, I have no idea what the method is when no start time is chosen.
I can't seem to find a definitive answer in the ESRI documentation.