Thank you for your question

I would definitely recommend to wait until your tank has fully cycled before adding macroalgae to your aquarium, as micro algae potentially can overgrow the newly added macroalgae too easily.

Once the cycling is done, and you have a nitrate level of at least 2ppm and phosphate of 0.02 ppm you are good to go :)

If you have any further questions please let me know.

Please stay safe and well.