Fixtures just load text data files (in JSON/XML/YAML) so, there’s no real way to insert dynamically generated data by just loading a fixture. On the other hand, you can get around this using other methods.
One option is the package django-fixture-generator where you can write python/django code to create data and it will be inserted before your tests are called.
Another option is a previous SO question: How to load sql fixture in Django for User model?. This has some code on using SQL files for fixtures, where you can use a SQL expression for your date requirements (e.g. GETDATE()+1 or similar in your SQL dialect).