(conjunction) 'as' in 'at the same time as when'

Question

This happened at the same time as when the window decorations disappeared.

I don't know the meaning of 'as' in 'at the same time as when' and the usage of 'as' in this situation.

What do you think of four sentences?

The first: This happened at the same time as when the window decorations disappeared.

The second:This happened at the same time as the window decorations disappeared.

The third: This happened at the same time as the time the window decorations disappeared. 

The fourth: This happened when the window decorations disappeared.

I think the first, the third, and the fourth are right, but the second is wrong.

I wonder how you feel.

Answer 1

As is used for comparison and here we compare two times, which are actually the same.

This happened at the same time as [the time when] the window decorations disappeared.

In your 1st and 3rd sentences the words when and the time after the conjunction are redundant. http://www.thesaurus.com/browse/at+the+same+time+as

The last sentence has a bit different meaning.

Answer 2

Using "as" for "that" is taken by many to be dialectal.

Try:

This happened at the same time /that/when/ the window decorations disappeared.

More informal:

This happened at the same time the window decorations disappeared.

Your sentences are too heavy.