There should be a note below the table that you are looking at.
As an example, the Cyclone IV sheet says:
--- Quote Start ---
(1) The incremental values for the settings are generally linear. For the exact values for each setting, use the latest version of the Quartus II software.
--- Quote End ---
Which means that there are "n" roughly linearly spaced steps from 0 to x/y for the delay in question (using your terminology). In other words, you've got "n" choices of what you want the setting to be, and the exact value is TBD (compile with the latest quartus and find out after the fact what it says you got).