Maybe not all types of contracting work for per day billing. For me I think it works as I'm paid to deliver a functioning product prototype that then goes to Q

Maybe not all types of contracting work for per day billing. For me I think it works as I'm paid to deliver a functioning product prototype that then goes to QA. Getting pulled into something urgent that required immediate attention is rare, very rare. So I can pretty easily predict how many hours I can devote a month out. But in your case, do you have to declare which days you allocate to a customer? I suppose if its sysadmin type stuff you may have a queue that the customer expects you to get to on or by a certain day.