If you mean to filter Tasks based on Deadline (date) field, then this is something we already addressed in our internal build. By default, when filtering is enabled for a date (or timestamp) field, you will have 2 boxes to narrow the results and include only dates withing certain range of dates (from - to).
However, for this to work, you will have to wait for the next release (should be available shortly) and you will have to enable filtering by the Deadline field:
Database, table task_field, row representing Deadline field, set filter=1
Or with single SQL query:
UPDATE task_field SET filter = 1 WHERE field = 'Deadline';
Kind regards,
Arek