Changing the date mid patrol
 

I found a thread on how to do this, changing it in Patrols_0

I changed the date when I was in port before I go out, I see the new date in the save screen to load, I load in and see the new the date.

Then when I go out on patrol it reverts back. what am I doing wrong?

I've done the same thing. The only way I can reliably change the date is using the Careers Option in Commander to set number of days in base.

I was changing date/time in base only between patrols in SH3 Commander, not mid patrol.