There is no limit to the number of daily on-demand backups that can be taken.
Up to 50 simultaneous table operations are allowed per account. These operations include CreateTable, UpdateTable, DeleteTable,UpdateTimeToLive, RestoreTableFromBackup, and RestoreTableToPointInTime.
The only exception is when you are creating a table with one or more secondary indexes. You can have up to 25 such requests running at a time; however, if the table or index specifications are complex, DynamoDB might temporarily reduce the number of concurrent operations.
The operation conflicts with the resource's availability. For example, you attempted to recreate an existing table, or tried to delete a table currently in the CREATING state.