Date & Time: Sept 7 4:03 AM Eastern
Frequency: weekly
World name: Excalibur
Character name: Deveryn Ev'liarsh
Area and coordinates: Island Sanctuary (Cropland)

I have been regularly harvesting / sowing crops every 48 hours from the cropland since Wednesday afternoon of August 31 at 3pm.
I repeated the process on Friday around 3:20pm.
Again I repeated the process on Sunday (Sept 3) around 8:45PM.
I was expecting to see my crops ready at 8:45PM on Tuesday (Sept 5) and I saw nothing.
I waited an hour. I waited a little longer.
Finally, I checked back at 4:00AM Wednesday (Sept 6) and my crops are ready, so it seems the timer for the blossom phase reset on Tuesday (Sept 5) at 4:00AM.