How should I store a simple, time dependent, repetitive data type in drupal
I think Webform is what you are looking for. You make a form that user(s) can fill in and submit. 

You can track the submissions over time, export them etc. There are lots of features you can do with webforms.

This is not a complete how-to for your question but you can take it as a start point. This way you don't create a node for each submission, but the form itself will be a node of type Webform.