too heavy in the P... P can lock out iron, so if you have a lot of P floating around these will lock out iron ions and the plant may struggle to find enough iron. then if the iron suffers the plant will have difficulty processing other nutes and so it goes on like dominoes. However it would take quite a lot to make this happen, but still best to err on the side of caution. Maybe use it once at the start of flower then again in the middle, although it all depends on your growing style. often when we give advice we only keep our own styles in mind.
I wouldn't use it at all. Although high P availability is directly linked to increased yields plants don't really need that much P, so having unused P laying around in the medium and then adding more will eventually lead to problems.