cache-block expiry maybe combined with heavy logic in those templates? It's default set to 2 hours, and you can set it to 0 if you want to make it never expire:
Thanks for your reply André.I tried to put cache-block in my templates.
But the response time is still very long (more than 30 sec. this morning) even for the first pages : login page and front page.
In the debug view, I can see that «Template processing» is taking the most of time. I don't understand that rendering such a simple template (front page) takes so much time.
During the day, the more I logout and login, the faster the front page is rendered.