Perhaps it is worth revisiting an old, trite but useful adage: "hope for the best, prepare for the worst."
Well, the worst, an allegation of misrepresentation, would not be good but, fortunately, that is not likely.
In any event, while sometimes a police certificate can be obtained in a short period of time, many times, for many countries, that is not the case. The U.S. FBI clearance, for example, cannot be obtained so quickly.
For the OP, here, it is what it is and it will take as long as it takes. Has to be done.
For many others who have already sent off their application, who checked "no" in response to the item asking whether they had been in another country for 183 or more days in the preceding four years (this is item 10.b in the application forms in use since October 11, 2017), but whose total absences add up to six months or more, time to REVIEW your presence calculation and add up the total of all days spent in another country during the previous four years, the total number of days COMBINED for the full four years.
If that even approaches, let alone exceeds 183 days, it would be prudent to consider initiating the process to obtain a police certificate SOONER rather than later, definitely sooner than the interview. Especially anyone for whom the country involved is one which will not provide a police certificate quickly.
Common error but it is an overt misstatement of fact:
Many applicants, it appears, have checked "no" in response to the item asking if they were in another country a total of 183 or more days, within the preceding FOUR (4) years, even though they were in fact in another country a total of 183 or more days during that time period.
As noted, actually the worst case scenario is an allegation of misrepresentation. The instructions for this item are straight-forward and clear. There is no hint that the question is about consecutive days in another country, about actually living/residing in another country, or about the total number of days in a calendar year. The guide provides several examples which more than amply illustrate the error in these approaches.
So far, however, IRCC appears receptive to "I misunderstood the question" explanations for checking "no" contrary to the facts. So there is NO reason to apprehend much risk of this triggering a denial of the application, for making a misrepresentation, which would result in a five year prohibition.
But anyone who is helping someone else prepare an application, please impress upon them the risks. Read the questions carefully. Avoid interpreting the questions based on what you think IRCC wants. Especially avoid interpreting questions in a way that makes it easier (such as to avoid having to go through the hassle and time it might take to obtain a police certificate). Answer the question that is asked and follow the instructions. It is all too easy to make mistakes as it is. Minimize the risks, focus on getting the question right, focus on giving an accurate and honest answer to the question asked, and follow the instructions.
Save the anxiety and headaches for some other aspect of life, recognizing there are plenty of risks that cannot be avoided, and no shortage of problems and burdens to endure. No need to add to them by trying to take shortcuts in a citizenship application.
the vn embassy does not offer that document.