Is not that medical schools will allow you or not, it's up to you, when you would want to take it, you just need the requirements from your school (TOR) to be sent to the ECFMG for you to be eligible for the exam. For USMLE Step 1- it covers coursework from 1st to 2nd year- so if you're planning to take the USMLE after 2nd year, you may do so, just register with the ECFMG and apply for the exam. Hope that helps.
I'm not yet a med student but I'm planning to start next year. So I am doing some research as well. Are you by any chance studying already?
PS: i'm a US resident, Filipino citizen and finished undergrad in the PI