I believe the watches( each being 3 hour in length) are as follows: 1st is 6pm to 9pm, 2nd is 9pm-12am, 3rd is 12am to 3am, 4th is 3am to 6am. then the days are devided into 12 hours 6am-6pm.(when jesus died about the ninth hour is was about 2 pm)(6a-7a is one, then 7a-8a,8a-9a(third hour),9a-10a,10a-11a,11a-12p(sixth hour) ,12p-1p,1p-2p,2p-3p(ninth hour),3p-4p,4p-5p,5p-6p(twelth hour).
 
Paul