HELP ASAP PLEASE PLEASE PLEASE. How much time is spent in each phase of the cell cycle? You will have slides of onion root tips where cells are undergoing mitosis. The slides are prepared by "fixing the cells and staining them. They are no longer dividing, but trapped in time. To determine the amount of time the cell spends in each phase, you will count the number of cells that are in observed in each phase. The total time for the cell cycle in an onion cell is 720 minutes (12 hours). To calculate the amount, this formula can be used: Number of cells in a specific phase Total number of cells counted X 720 minutes = time for specific phase.