a learner who can practise for about ten minutes a day may want to change lesson duration after a few weeks. What should we focus on first?

Treat the first weeks as useful evidence. If attention remains strong and goals are consistently unfinished, longer may help; if quality falls well before the end, more time may not be the solution. Ten focused minutes can be useful when the practice has one measurable purpose instead of trying to cover the whole lesson again. A trial or assessment lesson can help confirm whether the pace and teaching approach fit the learner.