120. Duration of powers.

The duration of a power, whether created to arise immediately or on a future event, is a matter of construction of the instrument creating it1. If, however, the power amounts to no more than an administrative direction to trustees, it is not within the rule against perpetuities2. Where the power is made exercisable, expressly or impliedly, during the continuance of the beneficial trusts declared by the instrument, then, so long as these beneficial trusts are valid within the rule, the power is validly exercisable until the effect of the settlement is spent and the estates under it become vested