Hi Kendall,
It is safest to use a dechlorinator with water changes. Leaving the water to stand will allow chlorine to dissipate but leave chloramines behind. In addition, the rate of chlorine dissipation is variable to ambient temperature and so a defined time length is difficult to predict. A dechlorinator will effectively remove chlorine, chloramines and can help detoxify the water. Some can also remove heavy metals.
Cheers.