Probably not very long at all!
>Wait until there's enough space between Juza and the doppelganger that a person could be inbetween them without being at "can immediately be punched" range of either, moving backwards if necessary.
>Then, stop time and run past the doppel, getting into said space between them and throwing however many spreads of knives at Juzawe can manage without exhausting ourselves, (up to 4 or 5) before unstopping time. If we can throw more than 2 than make one of them a stream directly at her; otherwise just try to cover space so she can't get out of the way in time.
>Once time unstops, be prepared to evade the doppel soon.
>...of course, if it doesn't seem like there's enough space, or that it'd be too hard to get into it and attack within the span of a timestop, just try to put some distance between the doppel whilst we think of a different plan.