If you have to stop Tai Chi Gung practice temporarily (for a phone call, for example), how long of an interruption can you have before you have to start back at the beginning?

If you can take the call and do figure 8s as you talk … indefinitely.
If the interruption has very little impact on your chi… as long as an hour.
Sometimes when I get interrupted, I’ll opt for figure 8s in the time I have left.
I go into figure 8s without warm ups just about every day, in any circumstance.
The sequence we do in class creates a crescendo effect… it sets up the most complete workout. Honor it when possible. Opt for figure 8s anytime.
Hope that helps.
Enjoy your day.
D