It says: "It is important to be aware that the Citizenship Act contains provisions that treat an application as abandoned if you do not contact IRCC with a reasonable explanation for not having your fingerprints taken with thirty (30) days of the date of this letter."
So, if you have a long vacation, I believe it is OK to have the fingerprints done a bit late with a letter and all travel info attached.
The whole FP process looks like:
1. FP in an agency
http://www.cic.gc.ca/english/citizenship/fingerprint.asp
2. RCMP will will do the search and provide a report (2-4 weeks)
3. Forward the report to the respective IRCC office
That will take a minimum 2 weeks plus logistic time. Hope IRCC will do other checks in parallel and not cause delays with FP.
Good luck to everyone in this tread.