I'm not sure how long it'll take...
I googled that with my 2nd loss and didn't really find much information because it varies from woman to woman. It'll seem to remain open for a while, that's why they say in the first 3 months after a loss a woman is more fertile because the cervix stays slightly open. Also Dr's say not to use tampons or have intercourse for a couple of weeks because of the risk of infection. (at least mine did)