Downtime is used to represent the time your character spends working when you are both on or off line.

You automatically get an income of downtime points each ic day which can be stored and used at any point in time. When downtime is spent it represents hours of time spent prior to the spending of the points.

For example:
When I learn a level of skill which costs 500 downtime it represents 500 hours of practicing and training in that skill.
When I farm the downtime cost represents the hours of weeding, seeding and plowing taken to produce that harvest.

The number of downtime points earned each day depends on a few factors such as how many energy points the character has. So a well fed character will earn more than a character on the verge of starvation.

A character continues to earn downtime points even when they are on the roster. This represents the fact that a rostered character is still around and working despite not being actively played. Therefore a character that has been on the roster for a long period of time will have a stockpile of downtime points that can be used to refresh the character.