Element <SOMETHING> is undefined in FORM.

[mars]

I am having problem with this statement how do you predefine
things? I am using HTML, COLD FUSION, SQL
Element CALLBACK_HR is undefined in FORM. The problem is this damn thing works after I click 'set' button on the FORM so
once I do that form.callback_hr gets defined so my question is
how can one predefine this variable or element form.callback_hr?

The Error Occurred in W:\Inetpub\wwwroot\BSF_test\ms_clock.cfm: line 31
29 : </select>
30 : <input type="submit" name="please_set_time" value="Set">
31 : <CFSET caBestCBTime = form.callback_hr >
32 : <CFSET #Client.caBestCBTime# = Timeformat(#caBestCBTime#, 'hh:mm tt') >
---------------------------------------
error above
CODE BELOW......
<form name="give_me_time" method="post" id="give_me_time">
<select name="callback_hr" id="callback_hr" >
<option selected value='10:00 AM' label="callback_hr"> 10:00 AM
<option value='11:00 AM'> 11:00 AM
</select>
<input type="submit" name="please_set_time" value="Set">
<CFSET caBestCBTime = form.callback_hr >
<CFSET #Client.caBestCBTime# = Timeformat(#caBestCBTime#, 'hh:mm tt') >
<CFSET caBestCBTime = CreateODBCtime(#Client.caBestCBTime#)>
</form>