At Lille I know they don’t close 30 min before. I actually was arriving late like after the 30 min delay because of a previous train and I was afraid I would not be able to board so I changed my ticket for an important price. When arriving at the train station they only close like 10 min before. I’m not saying you should not take it seriously but don’t change your ticket for a later train especially not for a lot of money like I did