Optimal Time for Marketing/Sales Event at Public Library

Explanation:

The earliest Sam can conduct a marketing/sales event at the library is at 9am, which is when the library opens. Sam's educational event is scheduled to start at 10am, so conducting the marketing/sales event before that time allows him to take advantage of the library's open hours. If he needs more time to set up, he can arrive even earlier, ensuring everything is ready before the educational event begins.