The lack of evening departure is common for new route launches, it's almost always early am dep, late morning arr for a quick turnaround for afternoon dep, then night arr that parks overnight for the early am dep. I guess they're seeing YYC-DEN as the market to tap into more than DEN-YYC.

Assuming airfare is competitive to United, Frontier would expand, but they can only expand so far. Unlike United, America West, American, or even Continental (which did YYC-EWR during summer), where else can F9 fly to N/S from YYC?