Calculate Seniority dates - process parameters

Summary

Calculate Seniority dates - Past period in days parameter - what to set to??

Content

We are converting from V1 to V3 for seniority dates.  We have set all of the rules and run the conversion process.  We are now trying to run the calculate seniority dates process, and are unsure what to se the "Past period in days" parameter to - it defaults to 1, but if I run it with that it does not seem to calculate all of the new rules we set up.  

If I use the "Recalculate seniority dates" button on an employee's seniority dates screen it runs the process back to the beginning of that person's history and then the rules we configured show up with the calculated dates.