I've had pretty good luck with this (
http://www.rackers.org/calcs.shtml) calculator. I'm usually able to get my mash within a few degrees using this. Also handy for calculating mash volumes.
The biggest thing for me was grossly underestimating how much time it would take to get a batch going. My first BIAB was started around 6-7 and I didn't get finished until about 3am (now a proud early morning brewer
![Big Grin :D :D](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
). The moral of the story is have everything possible already measured out so you're not planning as you're prepping.
You can get an extract batch done in a few hours...all grain is much more time consuming.
I've got it to the point now where the most time consuming thing I need to do is heat my strike water.