How do I set priorities for the future?
Type in your priority, select the drop down to set a priority for:
today / tomorrow
this week / next week
this month / next month
this quarter / next month
Why can't I set priorities for a day in the future, beyond tomorrow?
It's almost impossible to plan an invidual day in the future, but it is definitely possible to start thinking about your high levels priorities for next week or next month.
Instead, you can store a list of all your unsorted tasks, before you prioritise them. You can do this under the Tasks tab.