Hi there! We've been running Lucy Calkins' writer's workshop for several years now. We dedicate a minimum of 45 minutes every day for WW. I teach 2nd grade, so the focus is very much on literacy content.
I know what a struggle it is to try to fit it all in during a school week! In my classroom, these are my "core" time frames
Reader's workshop - 90 min.
Writer's workshop - 45 min.
Math Workshop - 60 minutes
There's a little extra time in each day that's flexible (after you subtract music, PE, etc.) for special units, social studies, science, cursive handwriting, etc.
What's great about Calkins writer's workshop is that her 2nd unit of study (in second grade) is focused on informational and scientific writing. So we are able to integrate science into our WW and that takes care of both at one time.
Social studies is fairly easy to tuck into reader's workshop while studying non-fiction text with biographies about famous Americans.
I hope this helps... good luck as you launch WW in your classroom. I love it, and can honestly say that my writers in the past few years have become much stronger through the WW program.
Cheers ~
Julie