I wanna simply answer: yes!!
You can reinvest whenever you want. The process is as simple as it gets. You can just do it either on the website or directly from your shareholder space.
The shares' value is fixed at 1€ and never changes to avoid any speculative effects. This means you can easily cumulate the number of shares you own each time you buy more. Pretty nice, hum?
Until we reach our 1 billion euros goal, it will be possible to buy shares at any time.