Putting more than one slice of bread in an electric toaster will generally make it toast slower. The reason for this is that the toaster's heating elements have a specific capacity to generate heat, and when you add more slices of bread, the heat is distributed among all the slices.
When you put multiple slices of bread in a toaster, the heat must be shared between them, which results in less heat per slice compared to toasting a single slice. As a result, the toasting process takes longer, and the individual slices may not toast as evenly as they would when toasting one slice at a time.
To achieve more consistent toasting results and faster toasting times, it is best to toast one slice of bread at a time in an electric toaster. If you need to toast multiple slices simultaneously, you can use a toaster with multiple slots, allowing each slice to receive its dedicated heat source.