I have used Hibiscus both in primary, secondary and both primary and secondary.
Get real hibiscus flower tea from a tea shop. Dont buy hibiscus tea from the grocery store, as its usually mixed with black teas and other things; its also never going to deliver the right potency youll need. Youll need a 300 gram (10 oz) packet of hibiscus
In Primary:
In a medium-sized pot, add 1 litre (Quart) of your water and the hibiscus, and bring to a strong simmer (try not to boil). Note that youll want to let this sit at least an hour to get a strong tea. Add to 1.5 litres of cool water and your honey and top up with more water if required in your jug.
In Secondary:
Add your tea to a sanitized brew sock or cheese cloth bag with a couple of marbles to sink it. After racking from primary just drop it in your Mead. I prefer 20 days. But check it after each 5 days to ensure it tastes as you would expect, don't be afraid to go longer if you want to. It will "mellow" a bit with age I like it slightly stronger than you would think.
I personally have settled on using both primary and secondary techniques above using 400 grams (14 oz) and splitting the tea equally between the two.
On a side note - I have found that for Melomels Hibiscus tea in primary brings great mouth feel and color that pair very well with Blackberries, strawberries, blueberries, and raspberries when added to secondary.