That means Proof of Stake will kick in after 45 days you keep your coins in wallet, you need also at least once in a while open wallet and leave 
synced to mature your coins (will take 45 days to start getting interest rate of 5%) If you still in doubt please google "Blackcoin bitcointalk" and 
read from page 135, BC is POW/POF after one week when proof of work was finished - that means all coins was mined Proof of Stake start. 
Hope that will help you understand how it works 
