How to use the online timer
Twenty minutes is about right for a single block of homework at primary age, and often for the early years of secondary too. Attention at that age does not hold much beyond it, and the last five minutes of a forty-minute stretch usually produce work that has to be done again anyway. Two short blocks with a proper break between them get more done than one long one, and cause far fewer arguments.
Setting up before the timer starts saves a good part of the twenty minutes. Book open, pencil found, tablet elsewhere, table cleared, and a room where the television is not audible. Children are pulled away by background distraction far more easily than adults, and a device within arm's reach costs more attention than most parents expect, even when it is switched off.
A visible countdown converts a vague and gloomy instruction into something finite, which is most of the battle with a child who does not want to start. Sitting nearby without hovering over every answer tends to work better than either supervising each line or leaving the room entirely. If a task is genuinely beyond them rather than merely dull, stopping at the end of the block and telling the teacher is more useful than a tearful hour.
Common questions
Twenty minutes seems short. Is it enough?
For primary age and the early years of secondary, usually yes. Two short blocks with a break between them produce more finished work than one long stretch, and far fewer arguments.
Should I sit with them while they work?
Sitting nearby without checking every answer tends to work better. Being in the room helps them stay on task, while hovering over each line turns the block into a negotiation.