That's the gist of it anyway.
I'll add that those numbers are reasonably close approximations based on what I've experienced growing many different indica/sativa hybrid variations, and a few pure strains as well. All of which has been supportive of what is advertised by reputable seeds companies in respect to flowering times. Meaning, when you buy seeds you should also be getting a reliable estimation on how long the flowering time is.
There's going to be a few exceptions to the rules here and there too. For instance, I've heard of atleast one fast finishing pure sativa, ~7 weeks IIRC. And I believe I've even seen some indica hybrids with very small percentages of sativa genetics, as little as ~10%, that take 8 weeks or more.
Of course, when you harvest is up to you. Some people follow their own schedules. Be wary of any claims of strains that finish flowering in less than 6 weeks though. Those are all going to be PURE BS! Until proven otherwise. Rule of thumb there = 42 days flowering MINIMUM, ANY strain.