4-man breakaway --
1 min @ FT, 3 min @ .7xFT, repeat ad nauseum.
To change things up, either have another virtual rider bridge up (add 1 min to the .7FT period) or drop one of the riders in the break (subtract 1 min from the .7FT).
I find that motivation and interest are higher if my longer trainer rides include some type of racing visualization.