If your declaration is "Schedule @slIdleStand", i.e. you want the script to be able to reassign the handle to point to a different object, then the second argument must be a pointer to a pointer to a Schedule object, e.g.

static Schedule *g_slIdleStandHandle = &slidleStand[0];  // Declared globally so the address of the variable is valid while the engine is valid
pEngine->RegisterGlobalProperty( "Schedule@ slIdleStand", &g_slIdleStandHandle );

Unfortunately there is no way for AngelScript to see the difference between one pointer to another, otherwise I would make AngelScript return an error if the property is registered incorrectly.

A handle is a pointer.

However, since you need want to register a property that is a handle, then you need to give the address of that handle, and not to the object it points to.