Most of the time T2T superman back extensions are done slowly on trainer's count. Not TODAY. Today, do as many full ROM extensions you can in the 20 sec "work" period. During the "rest" period, hold the UP (extended) position until the clock beeps to go again. If you must break a set, try to take the break during the 20 sec "work" phase. If you can, try hard to hold the UP position all the way through the 10 sec "rest."
Remember to switch hands on the High Windmills at 4. Here is the alt for the high windmill if you have shoulder flexibility issues.
Straighter legs are better on the v-ups.
Straighter arms and legs are better on the Supermans.
Be a little careful on those high windmills. Ease into them. If it's been a while since you did them, or if you aren't all the way warmed up, they could lead to roughed up hammys.