Lowmick wrote:When is best time to release ballast? On final glide or after it before landing?
The basic rule is: Keep as much water as you can for as long as you can.
If you have any water, and you reach final glide height, then you must keep all the water you have: Heavier = faster.
Always start with full water unless it is obvious from the weather settings etc. that the lift is weak. Even if you start with full water, fly 10km to the 1st thermal and then dump it all, you will have reached that thermal faster than without water, and at the same height (all other things being equal).
The really crucial and difficult decision is when to dump water if the lift is weak-moderate and/or hard to centre. In RL some gliders are a real handfull with full water and just don't climb well. Remember that with water you will normally have to fly faster in thermals than without. This makes your turn radius larger, and the effective thermal strength will usually be less.
It is all a compromise between amximum climb rate and maximum speed between thermals.