It depends on the result of the medical and what was in the questionnaire that he completed.
If there are any concerns at all, DVLA will write to his GP for information and this could take several weeks more, they allow the GP 6 weeks to send the reply back and whilst most doctors used to reply quite quickly, with the virus situation some practices are not prioritising completing forms.
If he doesn’t hear from DVLA in the next week it could be worth him asking DVLA about what is happening or, if he cannot get through on the phone, to ask his surgery if they have received a questionnaire from DVLA and politely ask them to fill it in and return it ASAP.