Feature suggestion: Adding custom named dates

#### To request a feature...

* Clearly describe the feature.
Allow the user to establish new named dates according to their needs, ideally through something as simple as adding a new line in the .taskrc file.
* Clearly state the use case. We are only interested in use cases, do not waste time with implementation details or suggested syntax.
For example, there are tasks I sometimes want to defer until I get off work. So I would like to add a "tonight" date that translates into "today at 17:30", so that I could quickly defer certain tasks by adding a wait:tonight attribute.
I understand I can use contexts to achieve something like this, but since my work/personal time schedules are extremely flexible, I'd rather see all my tasks on the same list and prioritize or defer as needed.