Leblanc's Ultimate - Transition Time?

Just played a couple games with Leblanc today, and did pretty well. One thing I noticed, however, was that Mimic does not appear to morph into your previous ability instantly. Is there a specific amount of time that it takes for Mimic to update?

Noticed this a few times when dashing in on enemies for a double Q (W-Q-R). Despite clearly dashing first, the mimic would be another dash or not cast at all.