You can use COEP, CO document line item table. It is the lowest level of detail. COEP will only have data after successfully posting to a WBS. But for CATS time transfers it does not contain the workdate, only the posting date of when the time was transferred.
Are you looking for individual time entry dates to a WBS?
RPSCO is the PS reporting structure table that should match COSS, COSP (the CO summarization tables) but doesn't always, hence transaction CJEN.