Can you 3d carve without using the roughing pass? i am not as concerned with the length of time as more in making sure that I misalign the bit when going between the roughing pass and the finishing pass.
You probably will not end up with the finished look you are looking for if you just run 1 pass. If you have your machine set up correctly you should not have any problems changing bits and not loosing your 0 for x and y.
What model CNC are you using?
Let’s address the issue of not being able to align the 2(or more) bits. I run multi Bit carves every day and they are perfectly aligned.
I don’t use this process, but Invetnables has put together a tutorial on 2 stage carving that discuses one method to ensure the bits are properly aligned. If you can let me know what model CNC you’re using ,there may be better, easier methods. BUT this method does work… https://inventables.zendesk.com/hc/en-us/articles/360012453174-Two-Stage-Carves-Roughing-and-Detail-Carves-
As to your original question.
Yes you can run the finishing only, but it’s up to you to setup the cut parameters so that they are not too aggressive to run it without a roughing though. It can work, it can also be a bit risky for broken bits or lost steps as well…
In some cases, you can finish with the same bit that you rough with. I have had projects where I use the same bit for both passes and programs like Vectric’s V-Carve can combine the two passes into one set of G-Code.