Imitation crab meat isn’t actually made from crab.  Instead, it is made from surimi which contains processed fish meat that is molded and dyed orange to look like crab.  You’ll want to follow general seafood guidelines and read the packaging instructions.  Fresh imitation crab meat can last around three days, while the same general timeframe holds once a can of pasteurized imitation crab meat has been opened - or when frozen imitation crab meat has been thawed.  As with all seafood, it is best consumed fresh (or when opened / thawed)