I don't grow C de B and there is some variation in when different Clematis within each pruning group start blooming, as well as environmental factors that may cause variation. I often have several kinds blooming by the last week in June and have a photo of Ville de Lyon blooming on June 5 one year that must have been an early one. I am about 80 or 85 miles north of Boston and in a colder zone as well, so I expect you should see blooms soon most years. Since this was planted last year, however, it may bloom less or later or even not at all this year depending on its size (especially the root ball) and age when planted.

Just an update to say I have three buds about to open, plus maybe a fourth one coming, as of June 16! Looking forward to seeing how it progresses.