An important contribution to the debate about "time limit" measures was made by Colin Harte in his book "Changing Unjust Laws Justly. Pro-Life Solidarity with "the Last and Least." Rather than attempt to summarise the book myself, I refer you to the Publisher's notice (Catholic University of America) and to an excellent Review by Francis Phillips.
The closely argued book is not by any means light reading but it is lucidly written and makes a vital contribution to the current debate. One of the most important sections of the book is the author's analysis of Evangelium Vitae n.73 (and n.90).