The latest issue of Bicycling Magazine (pix of race chick on cover) has what they are calling "911" workouts for people who just realized they have a major event (century, TT, MTB race) in 4 weeks. Some of the workouts, esp. for the TT prep, are about 1 hr and may be what you're looking for. HRM required, cadence helps (and the Cateye Astrale is usually on sale someplace, or use the gear calculator at sheldonbrown's website to figure out cadence vs speed for your gearing).