Usually medicals can be done the same day or within a few days, and then if the clinic is using the cic e-medicals system it takes seven to ten days to upload the results so that cic will be able to see them. We had ours done after receiving our PNP nomination certificate while we were waiting for the next EE draw, so that by the time we got our ITA our meds were uploaded and ready.
It is best to wait until you are close to getting an ITA to have meds done as you have to land within one year of the date of your medical exams I believe, so if you have them done too soon you have wasted money as you will have to have them done again. Same for PCC, it has to have been done within three months maximum of submitting your application after you receive ITA.