Translations:DC1/37/en
From Polyphasic Sleep Wiki
Not many adapted DC1 (non-extended) sleepers have been able to flex the core sleeps by much. It would require lower sleep requirements overall, or experienced sleepers to be able to manage a flexible DC1. With the second core fixed, the first core may be moved up to 1 hour forward or back. It is uncertain as to how flexible the nap can be. Regardless, more data is required to determine how flexible DC1 can be, compared to E2, whose second nap is highly flexible in a lot of adapted people.
