As it stands, the dropdown for the Prediction submission time is pretty restrictive; there's an erroneous gap between the shorter 2 and 5 minute options, the longer 20 and 30 minute options, and of course the highest limit of 30 minutes in itself.

While the dropdown is simpler to use in brief, having a custom field provides more flexibility for predictions, like a window being open for 2:30, 3:00, 12 minutes, 40 minutes, or a complete hour of submission time. Some repeatable prediction opportunities can have very predictable (no pun intended) potential submission windows and pay out times.

Here's a couple examples;

One I'm personally familiar with, before a streamer's scheduled time to go live, a prediction for guessing when they might start. Any time before then, the submission window can easily be an hour or more if the streamer is never early, thus making the highest 30 minute option restrictive.

Or Speedrunning, where Split One is almost exactly say, 3 minutes and 43 seconds long. You can have a prediction running for what happens in Split Two for exactly as long as Split 1 takes, a 3 minute and 43 second submission window.