It depends on your kids. When I taught K, read alouds, shared reading and word work were much more important than GR at the beginning of the year. When I taught 2^nd, my goal was to meet with my struggling readers at least three times each week and my advanced readers at least once each week. My students were grouped homogenously for GR. I was able to do two groups a day (most days) in a 50-minute reading workshop.

Here’s a possible schedule for a class with three GR groups: struggling students, students who are on-track, and students who are advanced.  Notice that the teacher does GR three days each week.  The amount of GR that students receive relates to their level of need.  And the students would pick their own group names; I would certainly not refer to any group of kids publicly as 'strugglers'. 

GR = guided reading, IR = independent reading, Resp. = reading response