D. binata, D. x hybrida, D. intermedia and D. filiformis have come easily out of dormancy a few weeks ago here in Iowa when the temps got above 50 degrees. (these were in an unheated shed "greenhouse" over the winter, so it's a little different than having them straight-up in a bog garden, but it's close enough. I haven't had any experience with D rotundifolia going dormant yet as I've only been growing this plant for a half year from leaf cuttings.
The Filiformis tends to flower earlier- spring to early summer, while D. intermedia will flower in the latter part of the summer and produce their largest, most robust flowers near the end of the growing season, when the temps begin to cool down.