The promotions can be open for as long as you wish.
If you have purchased a plan, you need to have the plan active to maintain the promotion active.
If you pay per promotion, your total cost of the promotion depends on the duration of the promotion. Duration is based on number of months. Example: If your promotion is 1 month (30 days) in duration or less you will pay for 1 month. If your promotion is 1 month and 1 day (31 days) to 2 months (60 days) in duration you will pay for 2 months etc. See prices per promotion. The duration of the promotion can be extended at any time.