How can a story be told in 4 parts if they're naturally told in 3?

I'm trying to write an hour-long episode for a TV show and I know you're supposed to tell episodes like these in 4 acts (~15 min each) but I'm having difficulty outlining it. If stories are naturally told in three parts, how are you supposed to tell it in four?

 

I'd say 'three-act structure' as a general guide is fine, but ultimately, whatever you are writing should have more than two cliffhanger moments. The best thing to do is watch some shows and pay attention to exactly how they are ending each act, and how this relates to the overall story of the episode. If you use the eight-point arc, ie

1. Stasis
2. Trigger
3. The quest
4. Surprise
5. Critical choice
6. Climax
7. Reversal
8. Resolution

Then two, four and six are the obvious breaking points.