When there are 3 minutes remaining or less, you can no longer change your roster, formation or tactics. You will not be able to boost morale and condition or heal players either. So consider how much time you need to make the changes you want and add 3 minutes

By the way, if the 3-hourly condition timer is running out during those 3 minutes, the condition will not be added to your team before the match, but after it.