It takes a long time for a top dressing and/or for most dry amendments to break down and become available to the plants. You can top dress well into flowering but the idea is to put what is needed in the container before it's actually needed. Give your plants water only after week 6 of flowering as a rule...usually by then fungal life has dominated the container and giving anything too radical can upset the balance. You can burn plants with organic nutrients especially with liquids w/ high NPK values as they are immediately available. Dry amendments take so long to be useful they typically cannot cause much havoc but it is possible to burn plants if you don't allow time for them to be "cooked" in or add too heavy. Always give 30 days of "cooking" time if you add amendments and compost to recycle your soil which I highly recommend.
Personally I would not give to plants anything with an NPK value higher than 5 in a soil grow but if I had to use up that hi P guano I would dilute a few pellets in a tea along with some kelp meal, EWC, and molasses. Earthworm castings are always good to add in any form whether on top, mixed in globally, or in an AACT. It's more likely that your soil lacks microbial activity which compost can provide than it is that your soil is deficient.
During early to mid flowering a top dressing of diatomaceous earth and garden gypsum is an awesome source of sulfur and other goodies like silica. Mix 1/4 cup of DE with 1 tsp of gypsum; adding a handful of EWC helps speed up the process.
Top dress by sprinkling the mixture around the outside perimeter of your pot about 2" in; you want to place your dressing away from the main stem. Again it takes time to work so you want to put it on a few weeks before it's needed in say week 2-3 of flowering.
