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What is spinup time? And do we need to use restart files for running the model post spinup?

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I would like to know what exactly the purpose of spinup time is.
Also, say if we want a 6 hour spinup, should we start the model six hours prior to the time when we actually want the model to begin?
Would that suffice or should we run the model for six hours, generate restart files at the end of the period and use those restart files to start the simulation that we are actually interested in?
I don't really understand how restart files work.
Please help me out.

The spin-up time is treated as the time period when the model physics and dynamics become more consistent and more reasonable. Spin-up is a more critical issue in global simulation, for example, the soil physics information must be consistent with the upper atmosphere.
In regional simulation, because the input data is severely constrained by large-scaling forcing, the spin-up is not that important.
If for some reason spin-up is important in your case, then your approach is correct. That is, you need to run the model 6 or 12 hours prior to the time when you need the model results. You don't have to use the restart function. Instead, you can simply run the model continuously, and discard the results for the spin-up period.
Hi Ming,
Thanks for the answer. It's super helpful.
But now I am not sure if I need a spinup time for my experiments.
Could you please tell me in what cases for a regional model will the spinup be essential?
My goal is to study the boundary layer and localized thunderstorms. How important is the spinup time in this case?

We usually don't consider spin-up issue for short-term, real-time weather forecast. For your case, if you are concerned of PBL and thunderstorm simulations, I don't think spin-up is necessary. Initial condition is more important.