The latest FO retention Bonus Window for pilots hired prior to 6/30/2016 ran from December 1 – February 28, 2018.
The FO Retention Bonus Payment for this window is required to be made no later than March 25, 2018.
Your last eligibility period runs 12/1/17-2/28/18, with your last retention bonus payment coming around 3/25/18

If you were hired after 6/30/2016, you must have completed probation prior to 12/1/17 (hired before 12/1/16) to be eligible for this most recent period. If you complete probation between 12/1/17 and 2/28/18 you won't be eligible until the next period starts on 3/1/18.
Reminder: you are eligible for all 8 retention payments upon completion of your probationary period (one year of service).