I also have LOTS of canna bulbs, but I start them inside so they are flowering by Mid may. Some cannas sprout very fast, and others very slow. My tallest one was planted in mid March and is now 2 feet tall. My smallest was planted 2 weeks ago and still does not have a leaf. You cant plant them outside too early because frost can get to them and they will hae to resprout again. It looks like a frost in your area from this point on is not going to happen, but it is not warm enough for fast growth. I take mine out in early May when temperatures are in the 70s and by then most of them are about 2 feet tall, and some of them are mature enough to flower.

Good Luck