Probably,, the wrong amount/too little waterproofer in the scratch coat, would have played a big part in the quick drying out of the top coat. Even though you gave the wall a good soak Sam, if you haven't put enough w/proofer in the scratch, the wall suction will soon dry out your top coat,,, plus the weather didn't help as the other guys have said.
Apart from it drying out too quick, you did a pretty good job of the render going by the looks of the pics, a nice even colour,, but as Micilin said the other week, if you go back over it and touch it up here and there, you change the colour,,, and you're right with what you said earlier,, useing a cement mixer gives the best results of all, and saves a lot of back breaking graft.
Here's another tip now you've got the w/proofer ratio sorted.
After you've scratch coated the wall (a day or two earlier) and it's now dried out and cured, ready for the top coat,, give it a soak down, then "let it drain off" for 5 to 10 minutes or so before you start putting on the top coat,, it's "not good", coating straight onto "soaking wet" scratch coat/lines.