With only 8 hours to complete this project from start to finish, time was short so shortcuts would need to be taken. Usually to freeze ice and prevent it going opaque, it is usually best to freeze it slowly and evenly over a period of 24 hours or more, having only around 7 hours of freezing time I would need to cut some corners.
I took a Coca Cola bottle and cut it in half, filled it with filtered water, fixing the stem of the rose in a piece of polystyrene and submerging the rose upside down in the bottle, resting the polystyrene on the bottle rim and putting it on the top shelf of the freezer. With any luck there should be enough time to freeze a few mm's of the outside wall solid, whilst keeping the inside liquid, this should keep it looking pretty clear.
The 3d printed part was a very simple and quick design, just a shallow cylinder with two walls, the inner wall to house the electronics, the outer wall to act as a small drip tray. I printed the base using 50% infill to make sure it was solid, strong and water-tight. Using a scrap piece of transparent acrylic I have left over from another project, I used a holesaw to cut the top cover, the LED strip is glued to the underside of this, I filled the pilot hole with some hot-melt glue to make it water tight (though you could remove the pilot drill and just cut with the circle) and also used hot-melt glue to fix the top cover to the base.
Now with the base printed, the electronics fitted and the top cover glued on, it was time to remove the coca cola bottle from the freezer and cut away the plastic, fortunately it was frozen with a good solid outer wall of ice, the shape was pretty good. I placed it on the base, switched it all on and to be fair it looked quite good, so not bad for a last-minute project.
Full instructions to make this project are available on Instructables.