Every sales team and every leader should be measured on results, and your part-time head of sales will help you set relevant KPIs for the business, your sales team, and the fractional leader themselves.
Additional factors you should consider are the responsibilities for your Part Time Sales Management role. This is typically much more than how to accomplish the objectives you have set.
Typically, we ourselves have helped most small companies with many time-consuming and unglamorous such as one on one meetings, finding and hiring new salespeople, sales coaching, and all the tasks a full-time manager would be responsible for.