Its always exciting to see your cacti bloom, especially when you've tended and waited several years for it to mature, obviously the reward of flowering or puping is the way it shows you its truely thriving. I was excited to see today (about 5 days) that the largest bud on my red crown has started to open. There should be at least 4 more (that I've noticed) to bud out.
While they are budding, I wait ever 3 to 4 days and use the cactus liquid fertilizer with a throughout soak place in sink without the bottom plastic capture cup and just water until it soaks in and do that twice, depending on the size of the pot. And use the miracle gro cactus fertilizer plant food (about 5-10 drops around the base of the stem, near the root). Every other 3-4 days I spray it with a water/food mix.
Example; first day saturate the soil at night with food, wait 3-4days spray to saturate the top soil, wait 3-4 days, saturate the soil. Never water your plants during the day. The beads of water can create a type of magnifying glass that will burn your plants.
Check out my Rebutia budding, pictures below.