It's unlikely that this is correct:
var date1 = component.find('HDate'+day+'__c').get('v.value');
because it appears to imply that your component is either iterating and generating a list of elements with
HDate2__c, or that the
aura:id of this component is dynamically derived from another component attribute.
aura:id values of the elements in your component are, and that
component.find() is not returning you a component.
component.find() can return
undefined, a single component, or n array of components, and you need to be prepared to handle those return values based on your component markup.