I do not see anything in 3.1.1 In-App Purchase that would forbid it.
Just take care of 3.1.2:
Apps that attempt to scam users will be removed from the App Store. This includes apps that attempt to trick users into purchasing a subscription under false pretenses or engage in bait-and-switch and scam practices; these will be removed from the App Store and you may be removed from the Apple Developer Program.
Also take care to inform user of how much time he/she would buy before completing transaction.
Topic:
App & System Services
SubTopic:
StoreKit
Tags: