A couple of mine are just starting to grow and I am in 6b. I find it depends on the type (2 vs 3 prune) and how much sun they get this early.

I would not worry at this point in zone 5a.

I am in zone 6 and I've seen the new growth buds appearing on the clematis already (group 3 and 2). We've had unusually warm temps here so I think they are a bit ahead of schedule.
All of mine are in full sun.

Julia

Out of the three, two of them have green leaves and lots of them already. The other one has none so think maybe I didn't mulch it enough.