You can schedule a green card medical exam before or after your green card application is filed. If before, then be sure that the civil surgeon signs it no more than 60 days before the green card application (Form I-485) is submitted,  If you choose to schedule after filing your green card application package, note that your medical exam results can be sent USCIS soon after submitting your green card application (Form I-485) or you can bring the results with you to your green card interview. NOTE: the results of the medical exam are valid for four years from when the doctor signed the form. Note the validity period is usually two years, but USCIS has temporarily extended the validity to four years to account for COVID-19 processing delays.