Problem rendering

[pls1]

I'm currently rendering an external concrete block wall which is part of a garden wall. I've read a few posts on here about the mix and application but its still proving quite challenging - mainly with the timing.
I did the scratch coat with a 4:1 mix with a splash of Rendamix. I wetted the wall first and applied, it went on easy but the first problem I found was that every now and again a few stones would break away from the concrete blocks and drag through the mix. This made it difficult to flatten and get the scratch coat completely level.
Also how long should the first coat be left before you try and level it out? I tried straight away but it dragged some of the mix off the wall. I tried again after a couple of hours but found the small stones would drag the mix off the wall.
Also does it matter if the scratch coat isn't level? Can I compensate with the final coat? How should the final coat be applied and leveled off & also the timings?

 

[brist]

Do not worry about the scratch coat to much, get it as flat as u can. The second coat is the critical one ,to level it off you rule it with a straight piece of wood or a feather edge rule. To float it up depends on the weathed conditions but you will know when its ready as the render will not drag around when floating.