Croissant dough issues

Hello, 

I've very new to bread baking and just tried making croissants again after a long hiatus. I'm not expecting great results due to a number of factors, but had some questions for next time. First, my dough was quite wrinkly and the mixing took way longer than the recipe (below) indicated.  It said to mix the ingredients with the paddle at low speed for about a minute, then switch to the dough hook and mix on medium for about five minutes until the dough was only slightly sticky and smooth. Mine took much longer than that, although I did end up switching to low medium (about a 4 on the stand mixer). Does anyone know what might affect the mixing time and why my dough was wrinkly?

Also, my butter. I thought I got the butter to a good consistency for the block (I beat the pieces with the rolling pin until they formed a rectangle that seemed malleable), but I still ended up with little to no lamination and just big chunks of butter poking out of the dough. Was my butter too cold? Not pliable enough? 

Here's the recipe (from the Joe Pastry blog):

For the dough (détrempe):

22 ounces (about 4 1/3 cups) bread flour
2 teaspoons salt
2 tablespoons sugar
4 teaspoons instant yeast
14 ounces (1 3/4 cups) whole milk at room temperature
3 ounces (1/3 cup + 1 tablespoon) cream at room temperature

For the butter slab:

3 Tbsp flour
12 ounces cold Euro-style (cultured) butter

Any tips would be welcome. Thank you.