I just wonder if I can set a delay action for some websites as I used to do that in previous version (6.8.x)...
like making the website loading for a while then appear to the user.
I don´t think we have a delay feature at the moment. But with 7.1.5 we have a "Throttle" Event, which causes the speed to be reduced. You can maybe try to set it to 1 kb/s and see if the page shows up very slowly. I am not aware if the throttling works good with small object, because we reduce the TCP window size, which may not work correctly with small objects, but maybe you want to give it a try.
the "Throttle" Event that Andre mentioned doesn't work very well with small object. In general it requires an object size of 1 MB or higher to work reliable, as it needs to adjust the speed during download. Objects that are very small will be downloaded too fast.