Nobody knows exactly, but I would say 4 months in advance to be guaranteed - maybe ok with 3 months at certain times- the timelines, as I have figured them out, are generally like this:
- to be safe allow 2 months for KCC to process applications. At quieter times it may be shorter but this is safer. I would not allow less than one month for processing.
- KCC generally schedules interviews almost two months in advance. The interview schedule seems to be finalised once a month, just before the visa bulletin comes out. So in early August for the October interviews.
So anyone who submitted later than early June may have missed out on a slot for October interviews. But as long as they submitted by early July they should be assured of a November interview.