Alternative system to the one offered by Twitch by offering by default the time that the predictions last
• Create a variable that allows both streamers and moderators to start predictions where they can freely define the time they last active. This time would be specified in seconds and when starting the prediction, the timer would be displayed, which indicates the remaining time.
The predefined options currently offered by Twitch are stark and lack a middle ground. A prediction can be very short or last too long, so much so that the message that the prediction has started is displayed for too long or too little time.

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Astagion commented
Update: In very simple words, a variable works like a blank box to which a number can be assigned. This number can be any number, which allows it to be adjusted to the tastes of the person initiating the prediction.
I add: to avoid abuse of the system, the minimum value of this variable can be set to 60 seconds (the minute that Twich proposes as the minimum duration of active predictions).