At Hongqiao, it's not enforced in the slightest (caveat: policies/enforcement can change on a dime in these parts). I know this because the colleague who accompanies me most often on the train is habitually slow, and ALWAYS picks up Subway or KFC before we get on the train (i.e. he would rather deal with the rebooking thing than go without edible food onboard). Due to the subway schedule (the train we take give us 8 minutes, total after we arrive at Hongqiao), and the fact that our trains leave from track 1 (furthest away), we hit the gate at T-1 pretty much every Friday we attempt this drill. We've only missed 2 trains during the course of the past year.