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I've always played it as happening on activation. There's no "may" or timing specification, so I figured it defaulted to immediate.
I'm going to throw out a general rule...
Artifacts (or covenants or curses used as artifacts) that have instant abilities that are not optional and do not specify a delayed trigger must be applied upon activation. Artifacts (or covenants or curses used as artifacts) that have instant abilities that are optional can be applied at any time their owner chooses so long as that time satisfies any other existing requirements.
Since you cannot activate it twice in same prep phase, I do not believe you can use it twice in same prep phase.
Repeating Kirk's question...So I am Creator now no longer works during battle if I make a RA with my only hero in play?