Does the existence of "gravitational waves" (assuming they exist) imply that time exists as a 4th dimension in the universe? I'm new to thinking about special and general relativity and I have no formal training as a physicist. However, I've been doing a bit of thinking about spacetime recently. I was wondering if "gravitational waves" provide evidence that spacetime accurately describes the structure of the universe. Or, in other words, do "gravitational waves" provide evidence that time exists as a 4th dimension in the universe (and what that implies  about past, present, and future events in 3D space all existing with equal reality)?
Please keep in mind, I'm not asking for opinions (or dogmatic assertions) about the accuracy of universe-as-spacetime-continuum theory per se. I'm asking if "gravitational waves" logically imply the universe-as-spacetime-continuum theory.
 A: Gravitational waves (GW) is one more phenomenon just like many other relativistic phenomena that confirm existence of spacetime (whatever it is defined as). Spacetime has already been confirmed for example, by atomic clocks having different tick rates on earth, and in orbits. There have been number of experiments including one done by NASA about frame dragging. GW was not necessary to prove spacetime. It was a prediction made by GR, which is now proved to be a fact per the recent observation.
A: The successful observation of gravitational waves$^1$ provides very strong support for the statement that Einstein's theory of general relativity accurately describes the behavior of masses interacting in our Universe.
The dimensional nature of time plays an important conceptual role in the arguments which lead to general relativity --- and, for that matter, special relativity, which has had many, many, many more successful tests.  
Any future theory of gravity must now predict gravitational waves, in addition to describing Mercury's orbital precession, centimeter-scale details of the libration of the moon, the aberration of starlight by the sun, gravitational lensing, length contraction and time dilaton, etc.
I am too cautious to rule out the possibility that some future paradigm shift will treat the time dimensions more differently from the space dimensions than relativity does.  But even if that happens, the relativity we have now will remain a powerful tool for thinking about the behavior of the world, just like Newton's outdated laws are such useful conceptual tools and give such useful approximations that most students still spend a year doing Newton before moving on to Einstein.

$^1$
Note that gravity waves are a little more prosaic.
