Usually it is open for one day only, but some people have been able to submit EOI up to 24 hours after the window closed and had those EOIs accepted.
You do not need to and should not send IELTS, ECA, etc. with your EOI submission. Those are for when you are submitting the full application.
Also, I don't know where this rumour has started that your CV needs to be in Canadian format. I have never come across this requirement and when I submitted my EOI and CV, it was not in Canadian format. The essentials of ANY CV is that you show your Educational qualifications, work experience, skills set and contact details, and provide a BRIEF summary of yourself as a professional.