How do I open the safe?

Hint 1 of 12:

In case you didn't know, the safe is in Dr. Fred's office, behind the
portrait.

Hint 2 of 12:

You will need to talk to several people in the present who can tell you
something about Dr. Fred and the safe.

Hint 3 of 12:

Nurse Edna will tell you that Dr. Fred opens the safe while he's
sleepwalking.  If only you could get him to go to sleep.

Hint 4 of 12:

Dr. Fred will tell you himself that he doesn't sleep because he makes
himself stay awake all of the time by drinking coffee.

Hint 5 of 12:

You should try to keep him from drinking caffeine.

Hint 6 of 12:

Just pour some decaf from the kitchen in his cup.