Simulation and Planning Time without any restriction.
Use the Simulation button for a launch, and beside a cost of the vessel, you will need to pay additional funds for a simulation.
After you finish your testing, use usual "Revert to Editor" option — you will get back a vessel's cost, but an additional payment will not be reverted (default - 2% of a vessel's cost). Do not forget to enable possibility to Revert in the stock settings.
For a "real" launch kerbals want "to plan" a vessel before the launch. Also you aren't suppose to revert the "real" launch after the planning, because they are "real".
For the planning time management Alarm Clock App is used. (changeable to KAC in the settings)
You make your vessel in the editor, click a Clock Button, and alarm is created (appended or prepended to your "planning queue")
Then you exit to the KSC and wait until the Planning Alarm is finished.
After that you finally Launch your vessel from the Editor or KSC Launchpad/Runway GUI with the usual Launch button. Alarm is deleted automatically.
If you have reusable stage — just remove temporally that stage from a rocket in the editor, create a timer, and then put stage back, and launch the vessel later.
If for some roleplay reason you have the ability to launch a vessel without the planning — just launch without planning.
If you want to make a small tweak to a vessel after the planning just before launch — go for it, the mod will not restrict you.
So, for example with the 6-hours day:
Alternatively, you could put a vessel's mass into equation in the settings.
Also you could enable some speedUps for having a planning time progression.
More info: https://forum.kerbalspaceprogram.com/index.php?/topic/183393-*
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