When to start looking for congressional nominations?

Hello everyone,

I couldn't think of a better placer than here to ask my semi-ignorant question: when should an applicant start applying for congressional nominations? I've done my fair share of research, and nowhere I found a clear cut date when I could start applying for them. Most of the dates I found were ambiguous: March/April ~ November.

Is it too late to start applying for nominations or am I just acting deliriously?

Thank you.