Can affiliate links or the affiliate program work only between two dates?

No. Simple Affiliate has no setting that turns referral links, discount codes, groups, or the affiliate program on or off on set dates. An affiliate's links and discount codes create referrals while the affiliate is active. To run a campaign between two dates, such as a sale, make the change yourself on the first day and on the last day.

Pay a campaign commission between two dates

1. On the first day, open Groups and open the group of the campaign affiliates.
2. Select the Commission tab, enter the campaign commission, and save the group.
3. On the last day, enter the earlier commission again and save the group.

A referral gets the commission that its group has when the order comes in, and keeps it after a later change. The change applies to each affiliate in the group. Product, collection, and new customer commissions replace the group's commission for the orders that they cover, and a Maximum commission amount limits the commission of each referral. If the group has them, change them too on both days.

Let affiliates refer only between two dates

Pending and suspended affiliates create no referrals from their links or discount codes.

1. Before the first day, keep the campaign affiliates in Pending approval. With Manual approval in Settings > Signup, new affiliates wait there until you approve them. An active affiliate cannot go back to Pending approval, so suspend an active affiliate before the first day instead.
2. On the first day, open Affiliates, select the affiliates, and click Approve.
3. On the last day, select the same affiliates and click Suspend.

Suspended affiliates cannot open their affiliate dashboard. Suspending also removes their connected customers and product attributions, and approving them again does not bring these back.

The conversion window is a different setting

The conversion window is the number of days after a referral link click during which an order counts as a referral: 30 days by default, from 1 to 90, on each group's Commission tab. It also sets how long a single-use discount code that a customer claims stays valid. It does not turn links on or off on set dates.