Thank you both. Given that I am cooking 1/3kg tonight, I am disinclined to give it the full 25 minutes; my sauce is recycled from numerous previous curries, so it will not get much cooking in the sauce, and I am therefore inclined to give it 15 minutes in the oven. I far prefer my chicken on the underdone side, so I prefer to err in the direction of undercooking rather than over.
Update : well, the end results were distinctly average. 15 minutes was, I think, 5 minutes too long for 1/3 kg, and obviously putting it in recycled curry sauce was not going to display its qualities at their best. It did indeed taste delicious straight from the baking tray. Tomorrow the remaining 5 pieces will be cooked in a fresh curry sauce; we'll see what difference that makes.
** Phil.