I have both species of Wal-mart apongentum bulbs, and they grow great! I have found about 8 out of 10 sprout successfully in anywhere from 24-72 hours. Some take a little longer. I have seen one sprout after a week. They'll grow in almost any conditions, tolerating both salt and very low light, and being roughed up by the fish. They also flower.
Useful Info based on my experiences:
1. Fish that push the bulbs around will slow down sprouting, rooting, and growth. If you plan on putting them in a tank with meddlesome fish--in my case a moonlight gourami and a CAE--pre-sprout them in an ordinary bowl with gravel on the bottom. Once they start developing roots, plant the roots in the substrate.
2. Sometimes, if another species of plant (ex, hygro difformis) starts growing rapidly, hogging up nutrients, apongentums will molt. They aren't dead, just leafless. This is the time when you break out the fertilzer. A few Flourish tabs will work wonders. Liquid fertilzers will also work, just not as well.
3. When buying new bulbs, look for packages containing bulbs that are large and plump. These bulbs have greater sprouting success.