Energy from $ t_{1} $ to $ t_{2} $
$ E = \int_{t_1}^{t_2}\!|x(t)|^2\ dt $
Average power in time interval from [$ t_{1},t_{2} $]:
$ P_{avg} = \frac{1}{{t_2}-{t_1}}\int_{t_1}^{t_2}\!|x(t)|^2\ dt $
