I will confirm this in the Washington DC Area.

During Rush-hour (morning or evening) I frequently arrive at my destination (30-40 minutes away) before getting HD Traffic information.  This makes HD Traffic worthless.  Other times of the day, nights and weekends - I usually get HD Traffic in a few minutes on the same routes.

It could be due to the large amount of traffic data during morning and evening commutes – but I wonder if TomTom data has a lower priority on the ATT Network?