EBS pricing model

Hello team, does anyone knows for sure if EBS Snapshot are charged proportionally across the month? I assume they are since this is how S3 and EBS volumes are charged.

Ex: if a customer creates a 10 GB Snapshot on April 30 he will be charged $1.3 (SA region so 0.13 GB/mo) or 1.3/30 = $0.04 ?

Thanks