They need to clarify the terms, it is unclear if this minimum usage is free or if they will cancel your account if you go over. These are both in their agreement:
"You also will be charged AWS’s standard rates for any use that exceeds the free usage amount provided under the Offer."
"You will become ineligible for the Offer if, ... (b) incur fees for use of the service that exceeds the free usage amount provided under the Offer. ..."
"You also will be charged AWS’s standard rates for any use that exceeds the free usage amount provided under the Offer."
"You will become ineligible for the Offer if, ... (b) incur fees for use of the service that exceeds the free usage amount provided under the Offer. ..."