Question: Time, when notification is shown is too much. How can I cut it?

Answer: 
There is no built-in way to change this duration.

If you really want to pursue the issue, a community member has been maintaining a [PPA with a special version of notify-osd](https://launchpad.net/~leolik/+archive/leolik) that allows for some customization via GConf. You're on your own if you decide to use it though; there is little to no support provided for software from [PPAs](https://askubuntu.com/questions/4983/what-are-ppas-and-how-do-i-use-them).
There is a patched version of Notify-OSD (as ændrük already mentioned) that is maintained in a PPA. To be able modify and configure notify-osd you have to add that PPA and ugprade to it's version.

```
sudo add-apt-repository ppa:leolik/leolik
sudo apt-get update && sudo apt-get upgrade

```

Then you have to add a second PPA to install a GUI for configuring Notify-OSD

```
sudo add-apt-repository ppa:amandeepgrewal/notifyosdconfig
sudo apt-get update && sudo apt-get install notifyosdconfig

```

I have been using both these PPA's and can confirm that they work =)