A TAF is published 4 times a day at 6 hour intervals. However if you look at the forecasts within a TAF one might be at a 4 hour interval and the next at an 8. Just look at this example:
TAF KPDK 071124Z 0712/0812 32009KT P6SM SKC FM071600 33011G18KT P6SM FEW045 FM080000 32008KT P6SM SKC
Why not publish at consistent intervals?