I was there at the right time (for finding Suicune: between 20 and 40 minutes past the hour). This was at about 12:30 last night when this started happening.
Changing times on the DS (like for DST) or moving the game card from one DS or another seem to be common reasons that in game time of day stuff doesn't work.
or I suppose another possiblity is that it wasn't 20 minutes past the hour on the DS clock.