Thank you for your answer.
I find another way to solve my problem. I don’t know if it can be useful for others but in case of :
I did it by “separating dimensions” of the position parameter for my layer/compo and then alt+clic to add the expression : posterizeTime(10); value+time*200
10 : if the number of frame per second. The smaller the number the more twitchy it gets.
value refers to the previous value you put in your position parameter
200 is the number you change to have you end position set correctly.
Thanks for your help anyway.