Cancelling a subscription only means that it will not renew when it reaches the end of its duration. Regardless of whether you have paid for a week, month or a year, you'll always keep your perks up until the subscription ends.
In practice, this means that if you buy a 1-year subscription on the 1st of January and decide to cancel your subscription the next week:
1) You’ll still have access to the subscription perks until the 31st of December
2) You won’t be charged another yearly subscription at the start of the next year