Like mentioned above it is prorated. You can definitely choose not to take it. They hire all year, seriously. The incoming CFIs will be here for a year to 1.5 years max, then theyre gone. About 10 new guys come per month, while 10 are also on their way out. The bonus however fluctuates depending on how in need they are of new cfis. They are currently in a period with tons of new students coming over the next six months and so the bonus reflects that.