There is a KB article which explains about snapshots here: VMware KB: Understanding virtual machine snapshots in VMware ESXi and ESX
The contributing factors on how long it is required to delete/consolidate a snapshot is listed here: VMware KB: Estimating the time required to consolidate snapshots for VMware ESX and VMware ESXi
Could you afford downtime on the application?
Please note there is a difference when deleting a snapshot between a powered on VM vs powered off VM
VMware KB: Delete all Snapshots and Consolidate Snapshots feature FAQ
Note: If the virtual machine is powered off, no additional free space is required and the process will complete faster as there is no need track writes and the additional snapshot and delta file are not created as part of the process.
There is also commands to monitor snapshot deletion: VMware KB: Commands to monitor snapshot deletion in ESX 2.5/3.x/4.x and ESXi 3.x/4.x/5.x
Don't forget to follow the snapshot best practices: VMware KB: Best practices for virtual machine snapshots in the VMware environment
Some of the important points to consider are:
- Snapshots are not backups
- Use no single snapshot for more than 24-72 hours
- An excessive number of delta files in a chain (caused by an excessive number of snapshots) or large delta files may cause decreased virtual machine and host performance.