The angle can be anything between $70°$ and $180°$ degrees, exclusive.
With so little information, there is a huge amount of flexibility in the shape. By placing $B$ a long way away from $AC$, we get $\angle BEC$ to just above $70°$, and $\angle EBC$ to almost $0°$, allowing us to choose $F$ to give an angle anywhere between $70°$ and $180°$.
This image shows $B$ a reasonably large distance away from $AC$, and $F$ in varying locations. $\angle EBC$ here is about $3°$, so $\angle BOC$ can be anywhere from $73°$ to $177°$ just by moving $F$.
