The longer they spend on a page the better as this usually means they have found what they are looking for and are reading the information. If they click on and then immediately off you have work to do on your site (or they landed there by accident).
By comparison, the bounce rate is the percentage of users who enter and then leave a site without looking at any of the pages. Were they there by accident or did your site bore them to tears so they took off for the hills?