Well spread your readings out as much as you can, but I would also take a set on one day as well to try and work out the reading error. Subtract 4 minutes for each degree east of Greenwich that you are (basically local noon is earlier the further East you are).
The controlled assessment doesn't have to be submitted until next May, so it's your teacher who is setting arbitrary timescales, but as she's the one who will presumably be supervising you writing it up, I suppose that's her call.
Good luck.