The FP+ lanes are not used during EMH so there is no guarantee you will be able to use the DAS. You can ask at the individual rides and it may be allowed.
In our experience it's been a bit hit and miss during EMH. You can't get a return time as the new machines they now use will not work until it reached regular park hours (we only do morning EMH), however some of the cast members let us go down the fastpass lane if there's a wait time less than 15-20 minutes. To be honest, I'm not sure all the cast members know the rules either so we just hope for the best.
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