Hi,
I know this thread is getting a tad old, but since no-one has answered it yet..
do you mean AI trains in a terminus? If so you need to add a waiting point on the AIs patch (right click on the AI path track to add one) and you need to place it a fair bit before the buffers, or it will disappear, the best way is to place it, if it disappears off the map, move it back and try again, its more trial and error.
You will need to enter a time (in seconds) so say around 300 seconds (5 minutes) should do, maybe longer depending how long you will be there for.
You can use this method at other stations if you want a train to sit there for a long duration.
Hope that makes sense
Cheers,
James.