“The pleasure, as with most bivvying is generally retrospecive” - from the couple of times I’ve spent the night in a bivvy bag, that’s very true! I don’t think I got too much sleep. I’ve also not wild camped in years, but I agree with all the above. We would do the same in terms of starting out late - you can then get away from the roads and crowds before you pitch up. Try to stay away from the most well known hills and walks, and if you’ve never wild camped before, maybe go on a recce walk first , to see if the ground matches your map reading, before committing to it.
Also, I found this site very interesting when I started.