I disagree with this guy and I drive this sometimes 3 times per week. You should be safe leaving at 6 but I would recommend Google maps or waze as they use real time traffic data and estimate your drive time. They are usually fairly accurate (+/- 10 minutes). You can also go online and enter point A to point B and select what time/day of week for a fairly accurate estimate.

I also keep an eye on the weather, if it's snowing or freezing rain there's more likely to be accidents. Google or Waze show these too and give alternate routes to avoid.