I've always had the best success with Grevillea grafts (onto G. robusta stock) done in late winter and early spring, while the wood is still dormant but ready to grow with the oncoming warmer weather. This is the same timing used by professional nursery growers.

Keep the newly grafted plants in a sheltered position outside, with filtered sun at most, until you're sure that the graft has "taken" and new growth is obvious.

They can be gradually introduced to full sun, but protected from extreme heat in their first year.

Good luck!

tried 6 grafts will see how they go

For Grevillea, G. Robusta has proved to be the most successful. You will need to watch for a continuity of growth from below the graft, which means G. Robusta is trying to take over. I've bought a number of grafted grevs over the years and that's been the main failure for most of those that did fail. Good luck with your grafts.