I usually do 90 MIN...I'm beginning to wonder if this is necessary...what is most common 60 MIN?
I go 60. If you aren't sure do an iodine test.
I do about 12 hours, give or take. I mash overnight in my coolers and drain the next morning. Works great.
I think 60 minutes is pretty standard. There has been much debate over the length a mash really needs for proper conversion. Some test show around 20-30 minutes and its pretty much complete.