Seniority Date Changes in R13

Summary

Can we continue to use Manage Work Relationship seniority dates after upgrade?

Content

We understand that customers should begin using the Manage Seniority Dates page and personalize out the seniority date fields on the Manage Work Relationship page.  I'm wondering if this needs to be done immediately upon upgrade to R13 or if it's possible to do after we come up for air.  We have a fair amount of work to do to update fast formulas, custom reports and eligibility profiles that use seniority dates and want to make sure we have the time to update and test.  If anyone has already started the change and has documentation or advice I'd also love