Ideally the basic exercises should be done when you first get up in the morning and right before going to bed at night. Done in the morning, they lengthen your muscles and prepare them for whatever you will be doing during the day. They refresh the brain-muscle connection to promote efficient and easy movement. Done at night, they release any tension that may have accumulated throughout the day, allowing you to sleep more relaxed.
There is no limit to when you can do the exercises, though. Many of the exercises can be done in a chair, and can thus be done at work or in any other place with a firm chair. It’s especially helpful to release tight muscles with some Somatics exercises right after doing an activity that you perceive is causing muscular stress (for example, weeding, heaving carrying, or long hours at the computer). That way the stress is immediately relieved and doesn’t have to result in sore muscles the next day.