I'm not sure I understand your question. If you assign a resource at 70% assignment units Project calculates work based upon Task Duration * Units. Assuming an 8 hour day - the resource's work is 11.2 hours.

If you want the resource to work the 11.2 hours in shorter time, assign the resource at 100% and specify the 11.2 hours of work. Project will recalculate the duration to 1.4 days.

Split your screen to show the Task Form in the lower pane and enter the work for each resource as you make the assignment.