Quick tip for GNOME/Unity users: If you want to add a delay to a startup application, the easiest way to do it is to add the "X-GNOME-Autostart-Delay" parameter to the application autostart desktop file.
X-GNOME-Autostart-Delay is supported by GNOME and Unity and won't work with Xfce, LXDE, KDE, etc.
To delay the startup of an application under Unity or GNOME, you need to edit its autostart desktop file. Here's what you need to do:
1. If the startup desktop file for the application you want to delay is located under /etc/xdg/autostart/, copy it to ~/.config/autostart/ (".config" is a hidden folder in your home directory so press CTRL + H to show hidden files/folders)
2. Open the autostart desktop file with a text editor (e.g.: open Gedit, then open your file manager, navigate to ~/.config/autostart/ and drag and drop the desktop file from the file manager to Gedit) and append the following line to that file:
(where "NN" is the number of seconds you want to delay the application startup by)
3. Save the file, log out and log back in - the application should autostart with the delay you've set under step 2.