Reminder: The requirement to submit a police clearance certificate WITH THE APPLICATION, which is triggered based on a total of 183 days presence in a particular country, adding up all periods of time during the four years prior to the date of the application (adding up each separate trip into one total), is merely an administrative criteria IRCC has established for determining which applicants are required to submit a clearance in order to make a complete application for citizenship.
As I have oft cautioned, IRCC has broad discretion to request additional documents and information relevant to any of the requirements for a grant of citizenship, including evidence tending to prove the applicant is NOT subject to any prohibition. In this context, the relevant prohibition is a criminal charge or conviction in another country EITHER within the four years prior to applying for citizenship, OR any time after applying before the oath is actually taken. Thus, even a brief trip to a country, BEFORE or AFTER applying, can potentially lead to IRCC requesting proof the applicant has NO criminal charges or convictions in that country.
As I have in particular cautioned on some occasions, it can be a mistake to focus on the exact number of days as if the 183 day threshold defines for certain who will need to submit a clearance.
I DO NOT know, with a lot of emphasis on NOT KNOWING, why the OP here has been asked to submit a clearance. BUT what I do know is that waiting a "few days" to get past the 183 day threshold (or, for that matter, otherwise having been close to that many days but not quite) ONLY means the individual is NOT necessarily required to submit a clearance WITH THE APPLICATION, BUT THAT DOES NOT NECESSARILY AVOID A LATER REQUEST FOR A CLEARANCE.
Is the later request reasonable? That depends on the particular circumstances.
Is it procedurally unfair to not make the request months after the interview? That depends on the particular circumstances (including what has triggered the request).
Is it a mistake? The fact the correspondence refers to the 183 days threshold does not adequately indicate a mistake. Correspondence like this from IRCC tends to have quite a lot of boilerplate that is not directly relevant. The generic Finger Print request makes reference to verifying the individual has no criminal record in Canada, even though many of those requests are actually triggered for other reasons.
WHAT to DO: As others suggest, foremost best to respond to IRCC timely and, assuming it is true, state that a proper application for a clearance has been made but it is not yet available, and that when it is obtained it will submitted. And if IRCC does not proceed to another step before the clearance is obtained, then of course do submit it as soon as it is obtained.
There is a chance IRCC will proceed without the clearance. Obviously, CSIS and/or visa office personnel can conduct inquiries to determine if an applicant has criminal charges or convictions abroad, and indeed are likely to do so if the applicant cannot promptly submit a clearance. And if those inquiries establish the applicant has no charges or convictions in that country, IRCC might proceed to make a decision on the application without waiting for the applicant to follow through in eventually submitting a clearance.
Of course IRCC is well familiar with how to obtain and how long it takes to obtain clearances from most countries in the world. So the explanation better be a truthful one.
And, of course, if indeed an applicant has criminal charges in another country that will constitute a prohibition. Citizenship denied. (Assuming it is a charge which, if committed in Canada, would constitute an indictable offence under Canadian law, which includes so-called hybrid offences which could be prosecuted either as an indictable offence or a summary offence, regardless of how it is handled in the other country.)
