We consider that they can be taken indefinitely.
After 3 or 4 months, if you wish, you could try to see if reducing the dose, or stopping completely, has any adverse effects.
If not, then you could take 2-4 weeks off of them if you wished before starting again.
We aren’t aware of any reasons that would be important to do, but having a short rest from any supplement may be worthwhile if you wish.