First of all which collagenase you are going to use for isolation matters. There are many types of collagenases available for tissue digestion. I used Collagen IV for mouse adipose (0.03%) (1:1 volume by volume of tissue) tissue. I will suggest that its better to aspirate the tissue in buffer and wash it then chop and keep it (1:1 with enzyme solution) for digestion (at least 1 hr at 37 C) then you will get cells single cell suspension.
I am working with isolation of mesenchymal stem cells from rat and mouse adipose tissue.After mincing the tissue i use collagenase type 2 from sigma in concentration of 2 mg/ml with 2 percent BSA dissolved in PBS and sterile filter. And 1 ratio of volume of tissue to 3 ratio of volume of the above digestion cocktail for 15 minute is fine for rat adipose tissue and 10 min is sufficient for mice adipose tissue.