I wouldn't exactly calculate it like that. It doesn't necessarily mean that the actual verification time for a changeset is decreasing that much.
The verification process itself can be (and often is these days) a processing pipeline in which the average/effective verification time per changeset can, indeed, decrease to insanely small amounts.
For example the processing pipeline can process multiple changesets simultaneouly. If you have, let's say, 60 proposed changes, each one of them touching a different file in a repository, you can combine them into an equivalent single uber-changeset touching 60 files. You could then process this uber-changeset through a verification step that takes, let's say, 1h. If the verification passes you obtain a speedup factor of x60 and an effective verification time per changeset of 1 min, even if the actual verification time was 1h. Granted, you'll lose some of the speedup when the verification fails and you need to perform bisections to identify the changeset at fault, but that's a different story.
Or you can have each of the changesets verified independently, through 60 1h verifications performed in parallel. Same effective verification time, but with a whole lot higher verification resource usage.
The point, I guess, is that there are ways of building processing pipelines which can greatly reduce the effective per-changeset verification times and still keep very large scale projects agile.
Another point to consider is the branching strategy. Those 6 months weren't the actual verification time. Most of that time was simply spent navigating through the branch spagetti and fighting the integration hell, just to propagate the fix into the proper shipping branch - effects of the waterfall development model which was considered the norm at the time.
Today CI/CD (the proper one, not the CI Theatre) and Trunk Based Development eliminate all that wasted time/effort and side-stepping, with the fix being virtually ready for delivery right from the moment it is integrated in the trunk - no unpredictable massive branch merging obstacles ever stand ahead of shipping.