Start with 2 keys per day. Each day work on a different key pair. The following sequence takes 12 days to complete a full cycle of all 24 major + minor keys.
You can add the Chromatic Scale to any of these keys, starting on the key note.
Note that enharmonic keys like C# and Cb major are skipped. These are identical to Db and B, respectively.
We can increase the difficulty with a sequence that includes more keys in one day, combining relative major + minor keys, reducing total cycle time to 6 days.
A more advanced sequence will go through all keys in 2 days, using parallel major + minor keys. It should only be done after the previous patterns can be played automatically from memory.
The most difficult cycle, playing all keys around the full Circle of 5ths in 1 day.