Database field types are plugins that exist in /mod/data/fields so you can develop new ones and add them to your site.
As a quick start:
- Copy one of the existing plugins
- Rename the folder to time
- Rename the class to data_field_time
- Start modifying to get what you want - there are two files and an image.
We have recently developed 3 new fields for a customer project to support restrictions of entries to particular groups of users for a personalised resource library and user tagging for a folksonomy approach in a more general library.
There are a couple of examples in the plugins database that you could look into: https://moodle.org/plugins/browse.php?list=category&id=15
Adding a new field type does require some development but can be sourced locally rather than requiring a core change.