I'm sorry for the slow reply.
Please try the following code, it will validate the Date field only if it was changed.
fd.spRendered(function(vue) {
var input = $(fd.field('Date').$el).find('input');
input.on("change paste keyup", function() {
if(fd.field('Date').value == null && fd.validators.length == 0) {
fd.field('Date').validators.push({
name: 'MyCustomValidator',
error: '',
validate: function(value) {
if (fd.field('Date').value == null) {
this.error = 'Please specify date';
return false;
}
return true;
}
});
}
});
});