I think the crux of the issue is the Avs play at perhaps the fastest pace in the NHL, and Bednar wants his defenseman moving their feet and making quick north south plays to get the puck out of the zone, and in transition up ice.
The step up in pace from the OHL/AHL to the NHL is a tough adjustment by itself, let alone doing it for the Avalanche with their pace, and this is really the first time Timmins has experienced it, outside his two games last year.
It's tough to execute plays properly, right off the bat, at NHL pace as a first year D man. It takes time, and we know Timmins has missed a ton of hockey.
That's why it's so special how quickly Girard, Makar, and Byram adjusted, and even Byram has had a few bumps in the road lately.