According the the lodestone company pages

* Players whose names are displayed under "Last Week's Heroes" and "Yesterday's Heroes" will not reappear in the same list for a certain duration, regardless of total company seals accumulated, in order to better recognize the efforts of a wider range of individuals.
Anyone know what the "certain duration" is? Did they change it when servers merged? Do you have to wait one week before you can be it again, or can you like only be a hero like, once a month?