training plan

Does anyone use a training plan that goes by minutes instead of miles? I trained this way for the Ironman last year and really liked this approach better. I was just wondering if it was ok to train for an ultra this way also.

my training plan generally consists of one day on, one day off, then one day of heavy drinking.
For best results, refrain from drinking 48 hours before an event.

I would also be very interested in this type of training schedule for 50 and 100 milers. Have performed an exhaustive Internet search but only can up with mileage based programs.