In terms of seasons, no, I don't think that there's a significant change in terms of when they start. There's typically a couple week variation every year. For example, where I live in Indiana is about two-three weeks behind where we were last year. That's normal.
That phrase typically refers to things further north of Indiana. For example, if you go to Minnesota, flowers that always bloom in April here start blooming in May there. Things naturally vary based on latitude.
If we start seeing flowers blooming in February in Indiana, that's when I'll be concerned.