What I would consider given your goals and time limitations, YMMV.
weekdays: 10 minute Warmup, 20 min threshold or slightly above, 5 min recovery, 20 min threshold or slightly above, 5 min. cooldown. ON BIKE YOU'LL BE USING FOR TT. I would do these on the trainer so you can fully control the workout, sucky, but probably more effective than trying to navigate the mean streets of bethesda for a specific workout with time restrictions.
weekends: saturday - 7 a.m. or 10 a.m. group ride, pick up the 7 on bradley blvd about 7:15 - 7:20, peal off after democracy sprint around 9:00 a.m., home by 9:15. 10 a.m., pick up on tuckerman around 11:00 a.m., peal off on Falls Road or tuckerman, where ever is nearer in bethesda to where you are to be home by 1:00 p.m. Use your road bike with no aerobars, bet pushed way beyond your threshold or comfort zones by local racers. This'll take care of the VO2Max and anaerobic capacity needs of your workouts, when/if you get dropped, try to catch up, that'll force you into TT mode. Either way is win/win.
sunday: 20 min. WU, TT practice of distance, intensity, and on equipment you'll be racing, finish up with endurance mile riding until you get home. Could do on the 10 a.m. route in reverse so you're making right turns and have less interuptions. (would be something like Macarthur->falls->river->seneca->esworthy->river).