Are these sale calves or are they directly from a dairy? If they are from a dairy and they got enough colostrum you shouldn't have any trouble. The biggest problem with baby calves is scours.
Hours? Calves slurp down their bottles in a matter of minutes, if that. What kind of calves are you getting and how old are they? What kind of bottles will you be using? Most people use the 2 qt suckle bottles but a Holstein calf really needs more milk than that. Most calves do. A Jersey...