I would start with the corals in a bucket of tank water then the live rock in another. Then the fish will be easier to catch, again in their own bucket (ice chest will work too). In a small tank like 55 gallon I would leave the sand and enough water to keep it covered. Try to keep from stirring up the sand unless you want to take this time to clean it. 4 hours should be no problem just reacclimate the animals before putting them back into the tank. I would start with the rock, new and your old water, corals then the fish.
Some of you livestock seem to be in too small of a aquarium. Most Sea Horse's will need a tank of 20 gallon and up depending on the species. While your tang will need a 70 gallon in a year or so.
Not one shred of evidence supports the notion that life is serious.