Revise the Time Box timings...

[chalmerlowe]

Feedback from Pycon 2018.

Identify a defined period of silence for each task to go with/in the Time Box >>> When the students are told to "GO!" it was hard to focus on tasks for some of the parts when the instructor immediately started speaking from beginning to end (i.e. Timebox 3/10 might mean... aim for 3 minutes of silence, 7 minutes of explanation and a total of 10 minutes)

NOTE: there is a related issue: #119