MEMO 

To: All staff
From: Spencer Cao
Date: November 23rd
Subject: Elevators' [1] Maintenance Arrangements [2] 

Since the two elevators have been used [3] for more than two years, we would like to arrange a have arranged regular maintenance for them from November 25th to Novermber November 31st.

During the maintenance, the two elevators will operate by turns and the elevators will not be avaliable available after 6 p.m.. [4]

The elevator operation operating times will get back return to the normal when the maintenance finishes. [5]

Best Regards,

Spencer

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[1] Because you have added an 's' to the noun 'elevator' and followed with a noun, you have formed a possessive.  Therefore, an apostrophe is needed and, since you're talking about two elevators, the apostrophe goes after the 's'.  An alternative is to not add the 's' at all.  Here are your options:

"Elevator Maintenance Arrangements" (general elevator maintenance)

"Elevator's Maintenance Arrangements" (maintenance of our one elevator)

"Elevators' Maintenance Arrangements" (maintenance of our multiple elevators)

[2] We generally refer to the 'arrangements' (plural) we have made.  In the question, the phrase was "special arrangement", which is different from "general" arrangements.  As an example:

"Are you going to holiday in Australia this year?"

"Yes, I have made the arrangements?"

"What happens with your dog, Bully?"

"I have made a special arrangement for him."

(I actually think the question is a little wrong, because the described arrangements are general, not special.)

[3] When we refer to the use of a large mechanical device, we say that it has "been in use" for a particular period of time.  As an example:

"The buses have been in use for five years."

We say this because a "used device" sounds like an old or outdated device.  Yet your phrase was not wrong, so I have not changed it.

[4] Punctuation is never "doubled up" like that.  Two different punctuation marks are okay, but not two identical punctuation marks.  For example:

"Are we going to the movie at 6 p.m.?"

"No, the movie starts at 5 p.m."

[5] This sentence doesn't really provide any information.  A better final sentence we be something like the following:

"If you have any questions, please contact the Department of Property Management."