In tissue from the intestinal epithelium of a frog, the following proportions of cells were found at each stage of the cell cycle:

Stage Proportion of Cells
Interphase 0.90
Prophase 0.04
Prometaphase 0.02
Metaphase 0.01
Anaphase 0.02
Telophase 0.01
If the entire cell cycle in frog epithelium cells requires 20 hours for completion, what is the average duration of each stage?