[rayjay]

Every new tank will vary as to when it will be ready to stock. Once you feel the cycle is complete then "challenge" the system by adding ammonia to bring the level of ammonia to at least 1 ppm but I prefer myself to 2 ppm. If the ammonia clears to zero overnight, the tank should be ready at that point. If not, let it run a bit more and challenge it again.
Best chances of success come from a species only tank. Each additional species of fish adds to the risk of introducing pathogens the seahorses haven't grown up with, and are susceptible to.
If you DO go that route, check on the compatibility of each species of fish for placing in a seahorse tank.
Remember too that water quality is a BIG issue with seahorse tanks, much more so than for a reef tank. Keeping the temperature between 68° and 74° can help in this matter as it inhibits excessive growth of nasty bacteria that can develop from the "dirty" water created by seahorses.