Hi Fermi,
Dipterostemon capitatus ssp. capitatus is found from Northern Mexico to Oregon. With this sort of range, in a diverse set of habitats, one can expect a good degree of genetic variability within the species. Even within El Dorado County, California and neighboring Sacramento County (where we are located) blooming time can vary, February at the lower elevations to June at the high elevation limit of the species. So, depending on where your accession came from most likely is governing its bloom time.
I am back farming full time these days, however things are getting well organized again. Hopefully there will be time for me to visit a population of Dipterostemon capitatus ssp. capitatus near its high elevation limit in El Dorado County. These will certainly bloom later in the season, even in our Sacramento garden, if the pattern with other Themidaceae species is followed. I am also aware of an extremely high elevation population of Brodiaea elegans ssp. elegans. This site is high in my list of priorities to visit. I finally had a major breeding breakthrough with some of our native Viola species. If everything goes well, I will show a progress report this spring starting with Viola sheltonii.