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.
Update: Cinnamon supports this as well and Linux Mint 17 with Cinnamon 2.2 has this built into Startup Applications but I'm not sure if this is a Mint-specific or Cinnamon-specific feature though:
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.