I read this on another thread;
"I want to add that if someone decides to do upfront meds, you should be smart about the timing. You should go for upfront meds soon after AOR but not too soon (around 3-4 months / depends on the current application processing times). The only case when upfront meds can delay your application is when you do your upfront meds, and then within days, you get the Medicals Request from CIC. I have seen this happening to some people, and their applications get delayed because when you go for upfront meds, the DMP assigns a IME specific to you. When CIC issues you an MR, they also assign you a IME. Now when you do your meds, it takes around two weeks to go into the CIC system, and if you get an MR before that, you now have 2 IMEs assigned to you. Now the Visa Officer will have to clear up the mess you made, and it will delay your application."
Another one:
"The problem is that if you don't have the medical request with the IME no, which your medicals need to get linked to on the online system, your medicals go into a "pool" where all medicals without IME are. They then have to manually go and look on this system for your and all dependents medicals and link it up to your IME once they issue it.
I was strongly advised NOT to do upfront meds as this may delay or complicate my case."