That hourglass depends on whether you look for differences or look for
similarities. The earliest cleavage stages differ in different
animals: holoblastic vs. meroblastic, radial vs. bilateral,
determinate vs. indeterminate. Diagrams illustrating these emphasize
these differences.
Ignoring those differences, there is a general trend in bilateral
animals: morula, blastula, bastrula. Vertebrate animals have
additional shared stages: neurula, pharyngula. Diagrams illustrating
these emphasize the similarities.
As you get more complex morphogenesis and organogenesis more and more
differences between animals becomes evident. However you still have
similarities. The whole Haeckel drawings controversy is because those
drawings emphasized the similarities by underplaying the differences.
The differences are real but so are the similarities.
Look carelessly and you can easily see the difference between bird and
mammal right from the onset. Look closely and you cannot readily see
the differences between various placental mammals for a substantial
length of time.