You always get lots of people saying that they didn't tutor. Mostly they mean they didn't pay for tutoring, not that they did no extra work at all.
Based on comments in other forums, the typical range in terms of quantity, seems to be
(1) literally do nothing
(2) start in the summer before Y6 and familiarise the child with the test format and materials. Can be anything from less than 1 hour a week to 1 hour a day in the school holidays.
(3) start during Y5 and either send their child to a tutor once a week or DIY tutor using bond books, Atom and other resources. This includes filling in minor gaps in knowledge. Probably about the same or slightly less time/effort as piano lessons. (This is the style most often recommended on specialist forums)
(4) start in Y4 or earlier, sometimes this is because they have realised that their child is unlikely cover all the relevant material in time or because they were a late reader. Again, about the same or slightly less time/effort as piano lessons.
(5) do a lot of work of extra work from a very young age, such classes plus 3 hours a week additional HW from Y3
Depending on the child, I personally think that any of (2),(3) or (4) is likely to mean that most children would have a decent chance of performing reasonably well for them. Doing (1) probably means that you're relying on your child being very bright and having an instinctive grasp for eg NVR. Doing (5) probably means you are relying on your child being very compliant and not burning out over a 3+ year haul.
Whether any child gets a place depends on their natural ability, whether they've had "enough" preparation for them, how well other children perform, and random chance on the day of the exam. All you can control is the preparation, and you only need to do "enough".
Drop the long sessions, and pick it up again in a few months. Maybe try a different style of preparation. In the meantime, encourage as much varied reading for pleasure as possible.