I phone called OINP today to confirm their 'rounds of NOI'. They actually said the exact opposite of what you said. They do NOT have a specefic time or rounds to send NOI. They said rounds are for EE only, and not for OINP. OINP employees constantly and continuously searching for candidates on EE pool, and sending NOI to candidates fitting certain criteria at their own time, according to their needs.
Of course, I asked what 'criteria' they use to send out these random NOI? He said that OINP works with different and hundred of 'stakeholders' whom they have access to EE profiles and willing to send NOI at their own discrete and according to their demand. So, really, those NOI are not random or by luck, nor do they have a round on its own. Also OINP doesn't have a "one-size fits all" or 1-2-3 set of criteria.
Based on his answer, another question was raised which was about the 'rounds within EE'. I asked, then "why I see some PNP # within some of the EE draws"?
He said that those NOI numbers are actually a collection or a sum of all invitations that are sent to all candidates for a certain period (ie. 1 Jan - 30 Apr) - those numbers are calculated AFTR all NOI of that period are sent.. So not for a one-time PNP invite round. Hope this clears out your doubts and everyone's.
Conclusion:
Meeting OINP minimum requirements automatically put you in Que for NOI at ANY TIME.