Problem: You know what needs to be done but don't know when to do it based on availability or what to prioritise.
Solution: Like with the deadline calendar and target date calendar, an option to link a task to a 'Diary/calendar' selecting start date and time through to end date and time. This would build a diary for the user of the task so they organise their week/month and have a clear idea of what they are doing each day.
Alerts could be set up so say if there is a task due within the next two week and the task hasn't been added to the task owners calendar they will be notified. You could have an option to disable this also.This also starts to give an understanding if work is over subscribed for the remaining time.
You can then plot or set up the users work hours and days so these become greyed out but with the ability to override (if say they were doing overtime) You could also have the ability to colour code the diary for holiday, calls, meetings etc..