Here goes my grain of salt: I have not noticed too much deviation on time, and if so, I don't care so much. What really troubles me is that if you issue the "wait for" command to happen some time during a run, and you save the session. When you come back, that time is gone and the vehicle sits there waiting for you to delete that "wait for" and issue a new one. Saving sessions do not save everything you do. Conversely, if you bring a train to a portal and while is in there (to be produced later) you save the session, it will not be produced when you open it again. I have been able to get around the first example, by running al my AI trains off schedule library. There everything runs as it should. Looks like you are new to this, but in fact I have been making observations about this for many years by now. And I don't talk about it anymore, so as not to fill the bag more than what it is.