Is it possible to say the time in 24 hour in Esperanto, like 22:34?
Yes, I think it is quite common to use the 24-hour system in Esperanto. I think your example would be pronounced:
Estas la dudek-dua kaj tridek kvar.
PMEG has an article about telling the time. According to to that, it is normal to say the minutes by just saying kaj and then the number of minutes. I guess Bertilow is suggesting to avoid phrases like “it’s half ten” because for different languages similar phrases to that can mean either 9:30 or 10:30. In that case you can just say “… kaj tridek” and there is no problem if you want to be extra precise and say “… kaj tridek kvar”.
Yes, it is. When I was in France (in the castle Grésillon) this was actually done. They would, for instance, announce that tagmanĝo estos je la dek-tria and la ekskurso komenciĝos je la dek-kvina.
Yes. In fact, the 24 hour system is much more common than the 12 hour system in Esperanto because it's clearer.
Yes, it's very possible. Note however that rather than 22:30, it's likely to see it written 22h30.