One of the things that is different on the iSeries from Windows is the DST setting. For a long time, making the change was a manual process done by the unlucky operator that works the Saturday graveyard shift. And woe to the operator that didn't bring down Domino so it could pick up the time change. That has changed with V5R3 so that now iSeries will automatically make the change - convenient now that we have the DST change coming.
But still, Domino on iSeries is special in that it needs to use the DSTLaw notes.ini setting to properly reflect the new DST dates, unlike other Domino OSes. Check out Technote: Daylight Saving Time (DST) 2007 information for Lotus Notes and Domino for the specifics (I'm sure you're all familiar with it by now).
Basically, iSeries Domino servers should have the following line added to their notes.ini files - with the Domino server stopped, of course.
DSTLaw=3, 2, 1, 11, 1, 1
Update: Corrected the setting to remove an extra character - thanks Chris!