The answer to this question largely depends on what you want covered. I know that sounds obvious, but if you think about it, what portion of your day requires the coverage of a professional photographer? Here are some things to think about when making this decision.
End Time: How much of the end of your reception do you actually need covered? Many of the dancing photos at the end look alike after about half an hour. If your reception has two and a half hours of dancing, that’s going to be redundant. Unless you have some super-special send-off planned, you don’t likely need me there for the entire reception. A common end time for me is based on about half an hour after the last “activity” is performed. Most of the time, that activity is the cake cutting. For example, if your cake cutting is at 10:00 and your reception goes to midnight, you only likely need me to be there until 10:30.
Once you know what time I should end the day with you, you can work backwards. If my end time is 10:30 and you have a nine hour package, that means I would start at 1:30pm. Is that enough time to cover everything you want photographed?
Start Time: How much of your getting ready process do you want covered? If you want to tell the entire day’s story, you’ll need for my start time to be earlier. But, if you only want the last hour or so of your getting ready process captured, you can reduce the number of hours in your package. You should consider travel time to your ceremony location as well. Let’s say your ceremony location is fifteen minutes from where you are getting ready. Let’s also assume the worst and give it twenty-five minutes, just in case. If your ceremony is at 2pm and you’re planning on arriving at 1:30, that means you’re probably going to leave the getting ready location at around 1pm. If you want me to cover the final hour of you getting ready (some detail shots of the dress before you put it on, some staged hair/makeup shots, details, things like that) then you should have me start at noon.
Working backwards from the last things you need me to cover in your reception, back to when you will need me to start, will give you an idea of how many hours you will need in your package.
The second photographer’s start and end time don’t have to be same as the primary. The second photographer is rarely needed for the same amount of time. Typically speaking, the second photographer covers the tail end of the getting ready process at the ceremony location, and sometimes get detail shots at the ceremony site prior to the ceremony start. They then cover the ceremony, cocktail hour (while your portraits might be being done), and the start of the reception. They help with documenting your guests at the tables and around the reception. They also help with the grand entrance, first dance, and perhaps parent dances. After that, they are not really needed.