try editing line 16 - 18:
$WAFV_Errors .= WAValidateDT((isset($_POST["Contact_me_group_Best_Time_to_Contact"])?$_POST["Contact_me_group_Best_Time_to_Contact"]:"") . "",true,"","","",false,"","","",false,5);
$WAFV_Errors .= WAValidateDT((isset($_POST["Contact_me_group_Earliest_time_to_Call_HH_MM"])?$_POST["Contact_me_group_Earliest_time_to_Call_HH_MM"]:"") . "",false,".*","","",true,"d{4}/(1[0-2]|0[1-9])/([12]d|3[0-1]|0[1-9])","","",false,6);
$WAFV_Errors .= WAValidateDT((isset($_POST["Contact_me_group_Latest_time_to_Call_HH_MM"])?$_POST["Contact_me_group_Latest_time_to_Call_HH_MM"]:"") . "",false,".*","","",true,"d{4}/(1[0-2]|0[1-9])/([12]d|3[0-1]|0[1-9])","","",false,7);
to:
$WAFV_Errors .= WAValidateDT((isset($_POST["Contact_me_group_Best_Time_to_Contact"])?$_POST["Contact_me_group_Best_Time_to_Contact"]:"") . "",true,".*","","",false,".*","","",false,5);
$WAFV_Errors .= WAValidateDT((isset($_POST["Contact_me_group_Earliest_time_to_Call_HH_MM"])?$_POST["Contact_me_group_Earliest_time_to_Call_HH_MM"]:"") . "",false,".*","","",true,"\b(1\d|2[0-3]|0?\d):[0-5]\d\b","","",false,6);
$WAFV_Errors .= WAValidateDT((isset($_POST["Contact_me_group_Latest_time_to_Call_HH_MM"])?$_POST["Contact_me_group_Latest_time_to_Call_HH_MM"]:"") . "",false,".*","","",true,"\b(1\d|2[0-3]|0?\d):[0-5]\d\b","","",false,7);