No, you cannot have a different backup schedule for individual VMs in the one ImageArchive subscription. For Virtual Data Centre customers we recommend using VDC Backup.
For VPS customers you will need to purchase a new ImageArchive subscription to run a different schedule.
This scenario typically occurs when you may have a VM that is critically important and you want to back it up every hour but other VMs in the VDC only require daily backups. In this scenario you would need to have one ImageArchive subscription for each schedule.