Acclimation issues show up in some inspections that I perform. The typical response from the builder or installer is that the flooring was acclimated in the building for two weeks, "just like the book says." In some inspection reports, the inspector states that the flooring was acclimated for two weeks, and then rules out any potential acclimation issues.
Acclimation is not a time thing. Acclimation is about getting the moisture content (MC) of the flooring right; that is, to something near the long-term expected levels for that building. If the indoor environment isn't right or the length of time is wrong, acclimation will still happen, but to the wrong moisture level. For example, the target (long-term expected) MC for my house is 8%. If I brought wood with a MC of 6% into my house in the winter when the indoor EMC was 6%, the wood acclimates to 6%, not the 8% I want. If I bring 9% MC wood into my house in the winter, it could acclimate to 6% rather than the desired 8%.
Bottom line is that we acclimate wood to a MC, not a length of time. First, the indoor EMC must be right. Then the wood must be left long enough to get near that EMC. This way, acclimation issues are kept to a minimum.
Note that some manufacturers have specific acclimation requirements. Always follow manufacturers' requirements, but realize that even then some acclimation-type issues may show up.