Apparently, the concentration is supposed to be as stated because it is the lecturer who prepared it. Since at room temperature and 29 deg, the rate of reaction of iodine with acetone is higher, less iodine is left so volume of thiosulfate that was required was less than 17mL.
For 15deg, the volumes at diff times were: 19 mL, 16.2mL, 13.1mL and 10 mL. When i calculated for the 19mL, i got conc of iodine 4.75E-3 M but my initial conc is 4.55E-3.
For 0 degrees, the volumes of thiosulfate are: 31.50, 27.80, 23.00, 22.60. For all those volumes, the concentration of iodine remaining become higher than initial.