it depends on how many stops you make along the way; but if I remember correctly, it's about 5 hours +/-. If you stop at every pullout, add another hour or 2.

It will be closer to 6 hours, non-stop.

Driving the Icefield Parkway will take about 3 hours (non-stop), then add about 45 minutes Lake Louise to Banff, then another hour and a bit to Calgary, and the last bit to the airport in the north east of the city depends on the traffic and the route you take.

Naturally the length of time can be longer depending on weather, or construction on any of the roads, and traffic even in the mountain parks, of course.

You would only need to stay in Calgary overnight if you had a morning flight out, otherwise you could stay in Banff for an early afternoon flight, or drive all the way from Jasper for a late afternoon/evening flight.