The statement that "snapshots generally take seconds to drop and create" is accurate. The key is generally
. There are cases where creating a snapshot can take a very long time. You need to make sure that if you schedule automatic snapshot creation, it isn't done while there are long running processes, such as a large index rebuild, in mid-execution. Any open transactions in the database get "rolled back" in the snapshot as part of the creation.
You can read more about that here: Database snapshots can take a long time to create
My blog: SQL Soldier
SQL Server Best Practices: SQL Server Best Practices
My book: Pro SQL Server 2008 Mirroring
Microsoft Certified Master: SQL Server, Data Platform MVP
Database Engineer at BlueMountain Capital Management