Blooming is a function of a hormonal response to decreased light and not a response to nutrients. You can feed all the bloom nutes you want to a plant under 18 hours of light and it will never bloom. The first couple weeks of flowering when the plant is stretching it is using far more nitrogen than anything else with rapid growth (the stretch phase). Cutting N and spiking P too early just increases the risk of nutrient antagonism, locking out nitrogen or other nutes.
Not saying it WILL fuck up your grow, but it can increase the risk of a fucked up grow.