High Ref Talic

For every effect you generate, a round is counted from the start of your action to the start of your next. This includes things such as when saves are rolled, when damage is applied (for example, sleep-smoke and entangling ectoplasm), when summoned creatures appear and disappear, when effects change, and the like.

The actual round is pretty much used only as an abstract, a sorta framework for everyone's turns to go in. There are a couple of exceptions, but, for the vast majority of actions and effects, "a round" is used to mean from the start of one action to the start of the next.

As such, the 5 foot step would be illegal.