I had a leak in my rear tire that the sealant took far too long to seal. Seemed like a pretty ordinary puncture that it just didn't want to seal. It did do a good job of putting a coat on my down tube. My eventual solution once I noted the tire was near flat was to rotate the tire to the six o'clock position, agitate, and wait. After some time I added air with a CO2 cartridge and went on. After another 20 miles I had to inflate again but at last when I got home it sealed.
Not much you can say that hasn't been said about the best tire sealant available. I've found that OrangeSeal works better than other brands for road tires. Still not always perfect seals, sometimes it takes adding some extra air or a plug but it is still superior.