If the condition is casual or mixed, it shall be sufficient if it happen or be fulfilled at any time before or after the death of the testator, unless he has provided otherwise.
Should it have existed or should it have been fulfilled at the time the will was executed and the testator was unaware thereof, it shall be deemed as complied with.
If he had knowledge thereof, the condition shall be considered fulfilled only when it is of such a nature that it can no longer exist or be complied with again. (796)