This is what I have so far but I cannot figure out how to set the default value to today's date if the parameter is not passed in the query string.
<ParameterBinding Name="meetingDay" Location="QueryString(meetingDay)" DefaultValue="???"/>
Looks like I have to use the Today CAML variable. I was able to do what I need with:
<ParameterBinding Name="Today" Location="QueryString(meetingDay);CAMLVariable" DefaultValue="CurrentDate"/>