Let me ask similar question that is already posted in this forum.

I ran a simple script that only submit one page only once for one user.
I notice a big page timer difference between the following 3.
1. In actual simulation for 1 user (overview report).
2. In try script. In info or statistic section (True log explorer).
3. Custom timer (Overview report).
Page timing obtained from 2 and 3 are much less compared to what I got in actual simulation.