From http://www.w3schools.com (Copyright Refsnes Data)

WML <timer> tag

The <timer> tag defines a card timer. The timer starts when the card is entered, and stops when you exit the card.

Note: It is not allowed with more than one timer element per card.

Note: The time unit of the timer is 1/10 of a second.

Note: This tag can be used with <card>, <onevent>, and <template> tags.

Syntax

<timer value="somevalue"/>

Attribute	Value	Description
value	cdata	REQUIRED. Sets the default value of the variable defined in the "name" attribute
name	nmtoken	Names the variable that is set with the value of the timer
class	cdata	Sets a class name for the element. The class name is case sensitive. An element can be connected to multiple classes. Multiple class names within the class attribute are separated by white space
id	id	Sets a unique name for the element

The example below will display "Hello World!" for 3 seconds, and then take you to the file "test.wml":

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>
<card ontimer="test.wml">
<timer value="30"/>
 <p>Hello World!</p>
</card>
</wml>