In divorce, the spouses' assets are divided unless separation of property was agreed. Without an agreement, participation in acquired property applies. Everything acquired during marriage, such as wages, is divided equally, except gifts, inheritances and items solely for personal use.
The inventory — which assets exist, such as a car, house or bank account — is determined at dissolution of the property regime. This generally occurs upon filing for divorce, though judicial separation may dissolve it earlier. Importantly, this date determines only the scope of assets, meaning which assets exist, not their value.
Value is then determined as at the divorce judgment. Many assets will show no significant change, but shares, for example, may differ enormously.
In short: Your account balance is generally determined by its value when the divorce judgment is issued.