To answer the question above directly I would always recommend you activate scheduling in TM, anyways as I know some of you might not want to do that for any reasons I want to give some hints what this will mean overall for your system. I also need to say that if you are running TM Basic Shipping on lower releases as 2020 you aren’t allowed to use the scheduler. Since 2020 you can use the Embedded Scheduling Version.
As the durations of travels are determined via LDDD during creation of a stage the travel durations will be filled on your stages independent of scheduling. Anyways it can happen that you start a travel of two hours at 00:00 but reach the target location at 01:00 as there will be no component taking care of respecting the travel durations anymore.
Basically, the loading duration will be zero seconds for whatever you load. Anyways there will be still a loading activity. As you deactivated scheduling for sure the system will not take care that the loading time is matching operating times of locations. The loading will always be done at the point of departure and arrival.
Whenever you create a freight order or assign a freight unit to an existing one new stops will get a default point in time. The system takes for this stop the famous SEL_TIME of the requirement document stop which reflects basically the most important time (from SAP thinking – logic in class /SCMTMS/CL_ TOR_D _STOP_AM method FILL_ SELECTION _TIME_PER _STOP) of the stop.
If you want to live without scheduler I would recommend to spend some time and thoughts in how to overrule the SEL_TIME of the requirement stops with a custom stop after modify determination.
In the Gantt chart you can move orders via drag and drop and thereby also define the time by choosing the drop position. For sure the function reacting is the scheduler and therefore it will not work. In the Gantt chart you even get a error message telling you to use the scheduler "Manual plan strategy &1 incompatible with Gantt chart; time not updated".
Sadly the Gantt chart cannot "know" that your planning strategy isn't containing scheduling - so if you created own once please include the parameter MP_SCH_FOL set to X.
Once again, I want to emphasize that I would use the scheduler in one or another shape. Rather then not use it at all I would either try to archive what ever is hindering you in scheduling via BadI or build yourself a very simple scheduling just looping over all stops using the first plan-trans-time as a starting point and adding the travel duration (disrespecting acceptable, required dates …).