You may think that the time of day and the formality of the wedding will determine the length of your train. You’re right to the extent that determine the length of your train. You’re right to the extent that there are rules regulating what is done, but I certainly don’t think you need to follow them to the letter. What’s important is that you choose a train that suits you and your location.
Dragging on the ground as they do, trains are not terribly compatible with outdoor weddings - from both a practical and aesthetic standpoint - thought a short train is fine, as long as you’re using an aisle runner. Another consideration is the length of the aisle. Let me tell you - if the aisle is short, your train may be at the back of the church while you’re at the alter. Not good. There’s a reason it’s called a cathedral train. A long train also means that you’ll need attendants to help manage it, so if you’ve chosen not to have attendants, don’t go ordering to twelve-foot train.
Finally, think about the train in proportion to your body. If you’re petite, you could be swallowed up by a long stain train. Opt instead for one that’s shorter and made of a lighter fabric such as organza, lace, netting, or silk charmeuse.
After the ceremony, the train is bustled or detached so it won’t get in the way at the reception. Some trains can also be looped over your finger, attached at the waist via buttons or hooks, or designed as separate overskirts that you remove for the receptions.
If you love the look of a train but find it too cumbersome, you can create the same effect with a long veil that trails behind you as you walk down the aisle. After the ceremony, you simply remove the veil - no bustling involved.