Can an entity in an entity-relationship diagram have more than one relationship? I am practicing drawing entity-relationsip diagrams and in the example it states "many employees work on a project, and employee can work many projects but can only be assigned to at most one project at a given time." Does the final statement after the "but" mean that there is another relationship?
It means that time is an essential component of the relationship.  It's telling you that there's a functional dependency (employee, time) -&gt; project.

In an entity-relationship diagram, I might model it like so:



I made it a weak entity dependent on Employee and with time as a weak key, but it's still a relationship between Employee and Project, hence a weak associative entity.