Eggs are small clear spheres. Infertile ones tend to go white after a while. The eggs, for Danios, barbs, tetras etc.), typically hatch in 24 hours at normal tank temperatures, longer if it is cooler. Important to remember though, after hatching, they feed on their yolk sack for up to a week, (depends on the temperature), before they become free swimming, at this stage, they are tiny shards of glass stuck to the side of the bucket or on the crud at the bottom.
Many a good spawn has been thrown out because people did not give the fry time to get to the more obvious free swimming stage. Another point is that although I said 24 hours for hatching, certain groups of fish can take MUCH longer, rainbows typically take 2 weeks to hatch and killies can be months.