In what stage does the cell spend most of its time?
Out of the traditional 5 phases (interphase, prophase, metaphase, anaphase, telophase; IPMAT) the cell spends most of its time in interphase.
Interphase is considered the "normal" time in the cell's life; it is when the cell is more or less devoted to its primary function, whatever that may be. Cell division, by comparison, is a relatively risky time in the cell's life, and it usually wants to get it done as quickly as possible. This is because spending an extended amount of time dividing can lead to a greater risk of errors in the process, as well as less time spent doing the cell's "normal" job, which would lead to progressively less reproduction or fitness over the lifetime of the cell or organism.
More biomechanical reasons include the fact that the chromosomes condense during mitosis, rendering protein production difficult or impossible because the DNA is no longer in an accessible form. Additionally, some cell structures degenerate or disappear during division, such as the nuclear envelope, the lack of which would, again, render the cell susceptible to errors if its DNA were actually in use at this time.