Just check the plants to see which look vigorous and which look like they need a rest. Usually I pick for perhaps a week then let the spears grow into fronds. Then I cut them down once they start to flower. Then I get some more harvest once they get going again. Perhaps 3 or 4 harvests per year. I use the cut down stems as fertiliser (chop n drop), adding some Organic Xtra or compost or minerals as the whim takes me. Keep up the water and you're good to go.