Hello,
To answer this we need to know what is the default work policy in the organization.
http://usermanual.clarizen.com/#work-policy-2
Work policy determines the relation between duration, work, and units (resource availability).
You choose which is fixed, then you may update the second, and the third will be automatically determined.
You CAN override the default calculated value. Thus you can have a task with a 1 day duration and 10 hours of work (though you will might need to adjust the resources)