She’d been assigned to a raid with Dean at one of Voldemort’s decoy houses to grab some of the plans for a London attack, as tipped off by Malfoy. She was to grab them and then leave to meet Harry and Lupin in London. Malfoy had given them a slot of time for when the decoy house would be empty, and originally they had planned to enter just then and not a moment more due to the tight time restrictions. But the raid was squeezed in before a second mission Hermione was to help Harry with and so they’d ended up going fifteen minutes earlier. 