Have you done bridal/formal makeup before?
Usually the mua goes by their own timings and calculates accordingly. There's no set standard as such because the service is so variable.
The reason I say this is because everyone uses different gear to perform makeup services and each adds his or her nuances to the task. For example, if you airbrush and I brush, our timings are going to be different and your bride may want something entirely from my bride etc. It is also for this reason why I only do one booking per any given day.
It is also very difficult to indicate average times and costs as times and prices are calculated individually and are affected by area, time of year, distance to travel, numbers and the client's requirements as well as your own experience and expertise.
For example, I had a bride who wanted a natural look with minimal maintenance. She took just under an hour.
Another bride who wanted a specific, intense look (gothic theme) took two and half hours.
Trials and proms are anything you or the client want them to be. Some brides want you in and out the door. Others want to make a girly do of it and will book you for five hours. Normally, my prom/formal/debs bookings are group. I have a maximum group number otherwise it just gets too wild and you're there all night...
Really, it just depends on what you want to do.
Hope this helps you somewhat.
