<p>This work investigates the optimal allocation of harvesting and sensing durations in a wireless communication system empowered by vibration energy harvesting and assisted by Reconfigurable Intelligent Surfaces (RIS). In environments where traditional power sources are limited or impractical, low-frequency mechanical vibrations from industrial or structural sources offer a sustainable alternative to energize wireless sensors. However, the intermittent and fluctuating nature of vibration energy introduces challenges in sustaining reliable communication. To overcome this, we model a time slotted protocol where each frame is divided into two phases: a vibration energy harvesting phase and a data transmission phase (sensing and communication). A RIS is deployed to dynamically enhance the signal strength and improve link reliability without requiring additional power at the sensor node. We derive closed form expressions for the outage probability and throughput as functions of the harvesting duration. From these expressions, we formulate an optimization problem that maximizes the average data rate while ensuring energy causality. Numerical results demonstrate that the integration of RIS significantly extends the operating range and that there exists a unique optimal harvesting duration which balances energy availability and communication efficiency.</p>