Is there a way to start the service without a start time so that the service is at the right time at the load and unload instruction?
Not that I'm aware of. I've always has to do trial and error. Although if there is a way I'd be very interested in knowing as well!
What I normaly do is set the time to simulated time for the first run. After that I can find out how long things take:
I ask because Matt said to my first timetable "Third - Those start times really need to be fixed. to clean the last bit of the log up. For your portal services you could just remove the times and have them auto-start after say a 2 minute delay, then it won't even worry about any timing issues for them and just have them hold for a minimum 2 minutes and then head off - which would be a good solution for almost all the issues of this type in the log file."
Not sure exactly without looking through the original post and log files as that context is missing. I guess if it's a service starting after the previous service has finished, you could just give what Matt suggested a try and see how it impacts things. Failing that, Bas' suggestion might be a good idea to work out how long it takes to get from portal to the platform in Hagen
The only solution is to measure the duration it takes for various formations, note it down and then subtract that duration from the scheduled arrival time. For the same portal to station (Messe/Deutz to Köln Hbf) the times can be different based on the specific consists used as they have different acceleration, motor strength, etc.