From my experience, the morning is the quietest time at YYC customs. It can be a mess later in the day when more of the Europe/US/Caribbean flights tend to arrive, but there generally aren't as many international morning arrivals. Baggage tends to be the limiting factor if you're checking a bag, as it's generally pretty slow.

Domestic security is a bit of a mess at YYC these days with the terminal construction, but if you have Nexus or are traveling in J, those lines can be a bit quicker. Walking distances aren't too bad, so it really depends on the lineup for customs, security and baggage. In my experience, the two more variable factors are baggage and domestic security.