syntax for xsl test statement

Hi,

I want to check a time of 12:00 AM.  What is the proper way to combine two statements ?

<xsl:when test="substring(ddwrt:FormatDate(@End,1033,12),9,3) =  AM and substring(ddwrt:FormatDate(@End,1033,12),9,3 =  12:00" >

Thanks

mhoran