According to Personal PR, the purpose of offer deadlines is to create a sense of urgency:
Deadlines. This really costs you nothing, but it heightens the sense
of urgency to your mailing. A specific cut-off date encourages people
to make a decision and respond. “This offer expires in two weeks” is
better than a no time-limit offer, but not as good as "This offer expires Friday, December 13, 20XX.
The majority of published special offer advertisements specify the exact date that the offer expires:
Subscribe today and receive a weekly helping of witty and entertaining
comment and analysis on politics, society and the arts. Offer ends 14
The date format varies:
- Save up to $1475 on select Dell technology. Offer ends September 30, 2007.
- 6 MONTHS NO INTEREST on orders $499.99 and up. Offer ends 6/29/05
- Offer ends 31/05/05
The year is sometimes truncated:
To get over 2,000 symbols Free, just pick up your copy of AutoCAD LT.
But hurry — this offer ends June 30th, and every hour you wait is time
you could be saving!
The phrase "Offer ends on [Date]", seems to be common, but the word on seems to be routinely dropped:
Discover how to improve your sleep habits at www.lunesta.com. Or call
1-800-Lunesta. Hurry! Offer ends May 31st!
At is not commonly used to indicate a deadline date unless a time is specified:
...such a period ends at midnight on the day bearing the same number
as the first...
The expression: Offer ends at 1 March, is not useful to indicate the end of an offer, and is probably an unprofessional flyer published by someone who does not speak English well.
Professional advertisers would likely point out diverging advantages and disadvantages of two common expressions:
Offer ends 1 March
Offer ends on 1 March
Government Executive, Volume 39, Issues 11-21, p. 25
U.S. News & World Report, Volume 138, p. 29
Law Institute Journal: The Official Organ of the Law Institute of Victoria, Volume 79, p. 5
The Canadian Architect, Volume 42, p. 52
The Canon law: Letter & Spirit : A Practical Guide to the Code of Canon Law, p. 113