In Black Panther the black panther of Wakanda consumes the heart shaped herb to gain powers. But what is the duration of that power?
If a black panther eats the herb once, will it be effective for his whole life?
And it's a high possibility that time period is infinite.
From MCU wikia,
Usage of the Heart-Shaped Herbs is seemingly limited to the royal family to allow them to better protect themselves and Wakanda. During the ritual combat in which any tribe or family member may challenge the heir for the throne, the heir must drink a serum to strip away the capabilities of the Heart-Shaped Herbs.
Once ingested, heart-shaped herb enhances it's user's abilities. from the same article,
The heart-shaped herb grants enhanced strength, mobility, stamina, endurance and instincts to those who consume it. There is a preparation able to negate the powers of the herbs, used to allow fair combat trials for the mantles of both Black Panther and King of Wakanda.
Those given powers will remain until it's user drinks another herb, that has the ability to remove the everything that heart-shaped orb provides.
Black Panther also revealed that ingestion of another herb can actually strip the Black Panther of his powers. This allows T'Challa to compete in ritual combat; the effect was almost instantaneous. T'Challa actually needed to ingest more of the Heart-Shaped Herb in order to recover his abilities.
In MCU, there were no indication that effects from heart-shaped herb will wear off at anytime and there was no indication that Black Panther needed to use heart-shaped orb time to time. only needed to use heart-shaped orb, if there was a challenge and Panther has to drink the other herb to strip off the powers given by hear-shaped orb.
I found another article on Collider, which has a detailed explanation about heart-shaped orb on comics.
As in MCU, rather Black Panther, the effects are permanent(will remain unless acted upon), effective unless worn out knowingly, as in case of using a potion to strip off the herb's effects.