Early medical never accelerate timeline. Even in 2019 several files got delayed. Even medical is valid for 1 year till landing in canada. Hence its absolutely Wrong decision to go for upfront without AOR. Just wastage of money without any cause. Even now overall processing timeline for provincial nominee change to 22 months those who already applied (as per CIC website. Now if due to pandemic new strains populating and restrictions are strictly applied. All suffers. We never escape from present realistic situation.
Yes, getting medical done before AOR is not a good choice. And yes, medical result will only last one year from the date you took it. If something comes up, you might need to retake it. Unless if you took the medical exam after medical request and the process took too long and the medical expred, IRCC will likely extend the medical so that you don't need to retake. There are applicants in 2019 that the medical is expired but didn't end up retaking.
Upfront medical will speed up the the medical pass by at least a week. If you make an appointment after gotten the medical request, you might only able to book one that weeks or a month later. Howver, if you can book a medical exam appointment and get it done on the next day from when you get your medical request, there might not be much different compare to upfront.
No one can guarantee upfront medical will get you to move faster but no one can confirm it does not as well. Everyone is different like people who got AOR later than I got but they got PAL, MR sooner than I got so even if for some people they seem moving faster because of he did upfront, that doesn't mean upfront will speed up the process for all people. No guarantee but a chance.
If upfront makes you feel better, you can do it, it is an option. If you don't feel good about it just ignore what people are saying.