In total honestly, it all depends on your oven and the size of your chicken (I see this firsthand teaching cooking classes in my clients' own kitchens). A smaller four-pound bird can cook in under an hour. But a larger one can take up to 90 minutes, even if you've butterflied it. A meat thermometer is the one and only surefire way to know when chicken is done. I like to take my meat out of the oven when it's a few degrees shy of the recommended temperature. Especially if you tent the chicken with foil, carryover cooking will raise its temperature a few more degrees as it rests.