We “officially” started March of Year 5, with a tutor twice a week. Aimed for an hour a day study time before summer and 1.5hrs a day Sept onwards though it averaged at an hour daily as DC carried on with all his sports as before (5 days a week).
DC is at state school so had no experience of exam techniques, no Reasoning and had a huge gap to fill in Maths and Literacy.
If I knew what I know now, I would start mid Y4, do a little (20 mins) everyday (Atom?) without pressure and set the pace early as I realised along the way DC was a late bloomer though he did well at the end so very proud of him.