When employees go into the ESS to request time off it only shows the balance as of the end of the pay period. This means an employee can go in and request hours (thinking they have them) and they don't know that they are actually in the negative until they run the accrual ledger report. So in essence the time off being showed on the timecard should reflect what is in the accrual ledger report. See the images for an example, if shy goes into the ESS she will see she has hours when she doesn't.
This is available in the new time off request page.