Give viewers the option of when to view ads
To prevent viewers being in a situation where they miss live stream content, give users an option to "View ads now instead of on the regular timer schedule", which would then reset the timer. Yes you have to view more ads, but you then are guaranteed ad-free content for the next X amount of time (whatever the current timer is set at for running ads).
i.e. Watching a speedrun, on PB pace, 20 minutes left in the stream, but there's an ad in 15 min. I really don't want to miss the end! I'll just play an ad now, deal with it, and then I'll have guaranteed ad-free viewing the rest of this PB run!
Putting this in the hands of viewers empowers them to have control over the ad experience and then they won't miss the great live content moments they know are coming!