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There are "pointer" files that are necessary for working with the logs (thus why the instructions state to copy $FWDIR/log/*.log* instead of $FWDIR/log/*.log.
I was mistaken that they are rebuilt automatically, you'd have to use fw repairlog (from the CLI) to do that.

As for whether the logs will get imported/indexed automatically, I would assume this would not be the case if you simply copied the files over.
Starting the reindexing process (as described in the SK) ensures this will be done.
The time will depend on the amount of logs, overall management/log server load, etc.
You will notice some increased CPU during this time, which will "back off" when other management processes need to use the CPU.
This is normal, expected behavior.