These delays are specified in the data sheet using the *SLn command. Whenever DataLoad encounters such a command it pauses for the specified time at that point in the load. For instance:
*NR *SL1 TAB
causes control to move to the next record (*NR), a pause of 1 second to occur (*SL1), and a TAB to be sent.
The delay value can be enclosed in brackets, E.g. *SL(1), and can be decimal or whole numbers, E.g. *SL(0.5).
These delays are most useful for situations not covered by the Preconfigured DataLoad delays. As such they will probably be used in one-off, particular situations. Try to avoid using them repeatedly in the data sheet otherwise it becomes very time consuming to change the delay when debugging or fine tuning.