To adjust for the fact that the position could be liquidated over several days, the following formula can be used:

$$\text{VaR}_t \times \sqrt{\frac{(1 + T)(1 + 2T)}{6T}}$$

The adjustment to the overnight VaR of the position is

$$\sqrt{\frac{(1 + 8)(1 + (2 \times 8))}{6 \times 8}} = 1.7854$$

This means that the trader should increase VaR by 79%.