Shema
When the minyan reaches the shema in shacharit:

• If you are between bar'chu and end of amida, simply:
  • Cover your eyes like everyone else, but don't say the shema line.
• If you are anywhere else:
  • Pause and, with everyone else, say the first two lines of the shema (Shema, Yisrael… and Baruch shem…), and then
  • Resume where you were.

Reason You may not interrupt your prayer between bar'chu and end of amida.

Amida
Situation  You are saying your amida in a minyan and it is close to the end of the fourth hour of the day.
What To Do  Do not pause, even if the leader says kaddish or kedusha, if doing so will delay you past the fourth hour.