To be fair, 100% isn't right. But relying on it is not a good idea. After OLCI it becomes more accurate, but it's really around 90 mins before departure that you really see what's going on. At T-60 EF no longer can show it and things are pretty final, but in those 30 mins between T-90 and T-60 you can get a really good idea of what's going to happen. Op-ups often happen at exactly T-60 (especially out of DXB), but I've had them as early as 6 hours before (while still enroute to DXB from CPT).

In J and F seat maps are more accurate of course, though with the new H (Special) fares in J they will become less accurate