[pygtk] A "delayed changed" signal for text entries?

[sandbox_mail]

Hi folks,
in my GUI I have an entry where the user is supposed to enter an 
expression according to a specific syntax.
If the user makes a mistake, the entry turn red.

This works quite well but there is one usability flaw:
Right now I use the "changed" signal to invoke checking of the contents. 
Therefore the entry turns red right after the first character has been 
entered.

Is there an elegant way (maybe another signal) to delay the checking? 
Like in a wordprocessor I would like to change the color only after no 
further typing was done for ~1 sec. or if the entry loses focus.

Thanks for any hints!

Freddy