Hi Yalgar,
There is no last date mentioned in the e-mail but i read following line.
- We are unable to issue a visa beyond the expiry date in your passport. Your passport must be valid for at least six months.
I think once " Ready for Visa " e-mail is received, IRCC will wait for passports for the lesser of passport expiry or 1 yr from Medical results. Once the applicant fails to send the passports before any one of above occurs, IRCC will either request a revised medical or instruct to submit new passports.