When creating a timeline it is so important to sit down with vendors. Certain vendors will take a specific amount of time out of your day and you need to be able to plan for this so that things run smoothly.
For example only the photographer knows how long it is going to take to photograph family portraits, bridal party portraits, and bride and groom portraits. Every photographer is different. Your make-up artist/ hair dresser will know how long it is going to take to do your make up and/or hair. Thus, when it comes to planning your wedding you need to consult with the different vendors to make sure you build in enough time and to make sure different vendors arrive at a good time so that the rest of the wedding runs without a glitch.