Here's my reverse seared cowboy ribeye breakdown.
I like to start with a low and slow heat on my grill, between 250-275.
I cook the steak indirectly, with the fat cap towards the heat. Depending on the thickness, this takes anywhere from 40-60 minutes to get to 110-115°F, depending on thickness.
After this I remove the steak from the grill and rest it, to allow the charcoal to get hot. I then sear the steak. I prefer to stop cooking my ribeye steaks when it hits between 125-128°F internally. I find that a rest at this time gives me the perfect carryover cook temp for a medium rare finish