Hi, I typically mix about 30% perlite to whatever my peat/compost-based potting soil is... It lightens up the soil and allows for more oxygen in the root area. If you are working in coir, I don't think it applies. As kush said, you can flower whenever you want. If you plan to pot up first, you might want to try for at least 10% perlite in the mix. The reason I didn't say 30% is because plants are funny things. If you change the root texture to allow for a chunkier mix, you may find the plant rebels on you and refuses to infiltrate into the new structure. Good luck!