Good question; I have wondered the same thing.

To be on the safe side, I'd worry.

Though a Rose garden just before flower buds open is almost enjoyable for me as a garden in full bloom.

I don't know about the science of it, but I can give you my opinion, based on my past experience - my impression is that basically, the big flush always comes at about the same time. Even if we have a cold spring, the roses seem to catch up once the weather warms; its just everything happens quicker and things tend to bloom all at once - or maybe it is due to the the light conditions, etc. Now, if we were to have an exceptionally cold May, that might slow things down; but so far, unless something really strange happens next month, my guess is we will be pretty much on schedule for bloom.

Ebharvey, I think it's a combination of sun angle/daylight hours, and the warmth and brightness of the days. My big rose flush can vary by about 3 weeks max, but we can't overcome latitude. We are far north in the US, so spring starts late no matter how hard I pray to the weather gods. I also have been comparing this spring's temps to last year's, and we are a whopping 10-20 degrees colder this year. However, when the earth's axis starts tilting steadily toward the sun, as summer comes on, we in the farther north experience a rapid onset of summer and very long sunny days for a short, intense growing season. You are in Southern New England, so your summer growing season would begin slightly sooner than ours. Our latitude is the same as Maine's. There's not a whole lot you can do about the weather. We even had some snow this morning, blowing in sideways no less. What next? Diane

If thaw/freeze causes the first buds to be lost, and the roses to have to make a second attempt, that could cause a delay. I echo Diane's comment, that there has been a 3 week variation here so far for me.