Well this is from the ICAO guidance on separation between arriving and departing aircraft on the same runway using LVP’s:
“The experience in some States is that to achieve this, the departing aircraft must commence its take-off run before the arriving aircraft reaches a point 6 NM from touchdown.”
In fairness it does say the spacing can be reduced to the departing aircraft being airborne before the arriving aircraft reaches 2nm where they have suffience surface movement radar to allow monitoring of the taxiing aircraft. I don’t know what kind of kit this airport had.