If you are planning a hospital birth, I am quite sure this question is on your mind. Is any time to early? Is any time to late? The answer is a bit complex, given we all have different expectations of labor and birth.
If your water breaks you need to go to the hospital. Your labor may not start right away or it could come on quickly after or you may already be in the middle of labor. Either way, when your water breaks you know your baby is headed into the world one way or another. It's time to head to the hospital.
Doctor's tell us that we need to go to the hospital when contractions are every 5 minutes for 1 hour. While sound advice, I have found many people are not yet in labor when they come in for this or they are still in early labor with frequent contractions that are not strong enough to dilate the cervix. If your contractions are strong and this frequent, then go to the hospital if you desire. With a first baby, it is likely you still have a ways to go with one hour of contractions like this. With subsequent babies, it is a good indication you are close. Pray and ask for wisdom if it's time for you to go.
If you are desiring an epidural for your labor, the above rule is a good one to follow as long as you are in active labor. If you are wanting to avoid an epidural, then stay home until you know it is close to time to deliver. You ask, "How do I know?" All I can say is, you will know. When you move into transition it is obvious. When you move from early/prodromal labor into active labor it is obvious. Pay attention. Pray throughout.
If you are in any doubt about whether you should go ahead to the hospital, call your doctor's office. Generally speaking, if you are contracting regularly they will tell you to go. That's just the way it is. Know, then, how you desire to proceed once at the hospital, and make your desires known.
How did you decide when to go to the hospital?