Riding at 100% (technically it should have been 105% if you were riding a 20 min test) does not mean that you can't ride after. 100% of threshold is just the power you can sustain continuously for 1ish hour of pedaling. After you finish your threshold work, it would be totally normal to be able to ride below threshold for appreciable periods of time, potentially hours. I once rode from Malibu to Santa Clarita. It was a cool morning, so I decide to ride up Latigo Cyn Rd as a TT interval Rode the first part at threshold- 49 min. Then a 2 min rest on the descent near the top and another 8 min interval at 93%. Then noodled home the remaining 55 miles at a leisurely pace over 4 hours, with a decent amount of climbing and headwind riding. Sure I was tired but I was fully functional.

Two by 20 at 105% is one of the hardest workouts I do, but when I'm in good TT shape I can get them done.