Maybe a book or some other source says specifically how much time took place between when Rey first started using the Force and when she arrived on Luke's island... but from the film, we don't know. JJ Abrams wrote Last Jedi into a corner by very specifically necessitating it pick up right where TFA smash cut to end credits. But what we don't know is the length of the trip to the island. The map looked like it spanned a rather significant portion of the galaxy, so how long did it take to get there? We don't know. Star Wars has always played loose with how fast hyperspace really is, with the most widely accepted speed being "however fast the plot requires."
Having said that, sure, her training definitely feels accelerated. But her demonstrated Force abilities so far are mind control and moving objects. She clearly had established combat proficiency long before she ever saw a Lightsaber. So that definitely feels earned to me.
How did Luke learn to fight? Were there frequent brawls over power converters at Tosche Station that we never saw? In the film, it certainly feels like Luke is only training with Yoda for a few days before rushing off and then actually not doing too poorly against Vader. OR we can hypothesize that it actually took some time to get to Bespin in a Falcon with a broken hyperdrive, and therefore Luke was training for awhile with Yoda (potentially learning something of Lightsaber combat).
The point being, it's not like Star Wars has never required fans to rationalize their suspension of disbelief before. It all boils down to what you're willing to go with. For me, Rey's abilities are not a deal breaker.
