Even though RSR isn't as crazy popular as when it first opened in 2012, you can still expect a decent wait anytime of the year. I would count on at least 50 minutes unless you go right at park opening. If you have EMH and you take advantage of it to ride RSR, that's even better. Now, since RSR is high-tech, it does break down quite often, and sometimes it has a late start in the morning or even extended maintenance that lasts until early afternoon. Thus, I recommend experiencing RSR as soon in your trip as possible, as if you wait too long, you might end up not getting to experience it at all.
Now, remember, even though RSR has very long stand-by waits, there is no need to ever wait in them. Unless you go at opening when the lines have not started to develop yet, do not wait stand-by. To minimize waits, use FP. Since disney changed the RSR fastpass system last June, you can now get fastpasses way later in the day than you could before. Still, if you want to be safe, try to get them before 11 am. If you happen to miss getting a FP, instead, hop in single rider. The wait there really depends, and I have heard it ranging from walk-on to 45 minutes. Still better than stand-by, though.
Also, take your time walking around enjoying the ambiance of carsland if you get the chance. It is such a magnificent place that one could spend a whole other day just soaking up the atmosphere!