I do not think there should be any defined timeframe. A little earlier, some of the questions that were asked had to do with whether this happens often. In the history of the Communications, Energy and Paperworkers Union of Canada, which represents 150,000 members across the country, the longest strike was the one in Lebel-sur-Quévillon, and the second longest was much shorter. This is not something that occurs frequently; these are exceptional cases. As a result, I do not think there should be a limit.
On April 21st, 2010. See this statement in context.