You would see an effect on the bryopsis, bleaching, in about 3 days with a spot treatment its much faster than mg however mg maintenance is a fairly well proven methodology as well it just takes longer.
This is my test environment, the very old reefbowl. peroxide tolerances reveal themselves quickly in a one gallon reef packed with established corals and tons of benthic life like brittles, asterinas, pods, live rock sabellids/sponges etc
spot treatments preserve them all. I included a snapshot of a green hair algae area I noticed in the bowl that was treated with one drop of peroxide while the bowl was drained for a water change yesterday. it will be dead by this weekend, reduced to just a green pigment on the rock which will go away in a week and reveal a clean area again. Winning the war on algae means catching all pests when they are new areas and not a growing community.
Treating with peroxide removes the initial mass of algae in my tank, and it only grows back once every three months or so. I don't have to manage water params to have an algae free tank they are just kept within normal levels. I don't even test for phosphate, just weekly water changes and spot treats as needed. I find clean up crews ineffective manual removal is thorough.
peroxide is used to clean the tiny niches in the bowl to keep it extremely clean of algae and to keep green haze off the glass. the coral growth only allows so much room to work in, but placing a drop of peroxide is always easy.