In general, let the first side (your pretty presentation side) cook undisturbed for 4 to 5 minutes. Turn the steaks and cook for 3 to 4 minutes for medium rare. Turn the steaks one last time and cook for about 1 more minute to reinforce the pretty first side.
If you want to enrich and baste with butter, lower the heat slightly during the last 1 to 2 minutes and add the butter pieces to the pan, and if you like, even the tops of the steaks, allowing them and drip down. Swab the steak in the butter or spoon the butter onto the steaks. The sides often need help so sear those briefly for about 30 seconds, too.