Once the cell is ready to multiply, it takes around 24 hours. Of course, you don't create 37 trillion new cells every morning. In reality, properly differentiated cells, such as neurons, frequently remain in G0 and never divide. You really don't want to hurt any of these.
Here is the breakdown by phase (post-G0):
G1 ~ 10 hours | S ~ 5–6 hours | G2 ~ 3–4 hours | M ~ 2 hours
Notice that the the actual process of division is far shorter than interphase. This makes sense since in principle, it generally takes more time to grow than divide.