Go to Offer box and click Create on Specific Offer
Select one or more countries as you want then choose the Shipping fee and time or Select Group Country.
Please refer this article on how to apply a group of country in an offer
Compose the offer and choose the Currency settings and Time settings you want
Enable Schedule to show the offer at a certain time.
Create offer and you can choose to publish the offer or not
Then you can check how your offer box appears on store
If you need some more helps, please feel free to contact us via live chat or email us at firstname.lastname@example.org