The hummingbirds that migrate to North America for nesting will be raising young from April to June depending on where you live (possibly earlier in the south & southwest). A female will use the same nest for subsequent broods in the same year, and will sometimes come back to the same nest year to year.

Depends on the species. The non-migratory Anna's hummingbirds along the Pacific coast as far north as BC can nest as early as Dec/Jan. In my yard (western OR), the males are in full blooming plumage about then.