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"...pick a group or three: International Hit-Wizards ... Fate herself; the goblins..."

Ooh! Ooh! You forgot The Founders! I know I've seen that one used somewhere!

Quite an impressive retrospective on Post-OP fanfic you've got there; you even got The Blot's Mr Black. I'm sure Loralee will be touched by Snape's shudder at 'the goblins'. You know, you could have strung this out the way Clell did the "how did you vanquish Voldemort" question, one or two per chapter.

Given your hint, when Harry blurred for a moment while chatting with Millicent, I'll guess that Hogwarts, which, as a magical construct, is quite capable of using the magic operating nominally within the Room of Requirement anywhere within itself without hard time-constraints, and that Harry, when he immerses himself into that magic as he did to leave Snape's presence, can both direct its manifestation and manifest himself through it; the blur was a time-disjunct splicepoint.

Of course, that's probably not the answer you're using, but it was fun coming up with it. Pray continue.