Interesting question... no, there isn't.
Everything's too relative to measure.

Eg. try this in an LD:
Walk across a room, measuring the number of strides
Now do it again.
Different, right?

Time would have the same trickiness in measuring.
Time seems to dilate depending on (1) the reality of it (2) your sleep state/depth (3) the stressfulness of the dream. I'm sure there's other reasons too.

It'd be great to find a way of measuring things. The eye movement isn't a bad idea, but isn't very helpful to the average LDer.