Auto-add today's date and time to new Entity title upon creation?
Option #1

For Drupal 7 you're looking at the Automatic Entity Label module if you're after a particular entity.


  "Automatic Entity Label" is a small and efficient module that allows
  hiding of entity label fields. To prevent empty labels it can be
  configured to generate the label automatically by a given pattern.


Possible option #2

Another option is available if your Entity has actions exposed to Rules.  Simple create a rul that reacts on entity creation, and set some conditions as per usual.  Then, in the actions do the following:

1) Add an action for Set data value

2) Find your entity (node for example) and look for :title under data selector (e.g. node:title)

3) Click continue

4) On the next page, set the data value to be whatever you need with tokens (so your example could be something like as [node:title] - [site:current-date])