The position of Zipcar Ambassador or other student ambassador decision are generally just for full-time undergraduate and graduate students so generally only 10-12 hours is required per week. Social media posting and planning is also required which is not included in that 10-12 hours.
Campus Ambassadors for Riddle and Bloom represent a company, like SweeTarts and helps put on different events to create brand and product awareness. These events could be as informal as giving a brief announcement at a student organization meeting, or as large as a company sponsored event.