You'll be happy you install them both at the same time. I did it that way, and the install basically goes hand in hand, and you won't have to mess around with taking off the stock turn signals, etc. There is a very good how-to on this site somewhere on the Evotech install, highly recommend looking at that before/during your install. It helped me greatly.
Overall it took me 90 minutes, but I took my time. After doing it once, I could probably have it done in half the time. The hardest part for me was removing the plastic nut from the seat lock mechanism.