DS32EL0421: DS32EL0421 Serializer Propagation Delay issue

We debug the Serializer Propagation Delay of DS32EL0421, choice as below :

1, 1   3 clocks – – – 5 – 6 clocks 2 clocks 10 – 11 clocks   (page 18 )  , the delay time is different every time , if i want to get the same delay time , what can i do ? thanks!