I have heard that lunch time can vary depending on force majeure. I have not personally encountered such a thing, but perhaps you have experience you can share? What does the length of lunch in test cricket depend on?

I have read a lot about the rules of Test cricket and such circumstances are given a lot of attention. According to the International Cricket Council the answer how long is lunch break in test cricket is 40 minutes, but the start of the break itself can vary depending on weather conditions or player injuries. The umpires will then be guided by the general state of play and their decision will determine the start and end of the break.