It was announced today that gravitational waves were discovered.

The article gives the following explanation of the experiment:

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When a gravitational wave passes LIGO, the tunnels deform slightly and the distance travelled by each beam changes so that they no longer cancel out.

I assume this "deformation" is space dilation, but does it also not cause time dilation? How do the effects combine to push the lasers out of phase? And why did it take until now to directly measure them?