I know `CREATE INDEX CONCURRENTLY` is slower, but how many longer it will takes to finish in comparison with the traditional `CREATE INDEX`? 40% more or much more than that?

I am creating an index in a table with 10000 registers, and in a column with 15 chars. It is taking 10 minutes using the traditional `CREATE INDEX`. 

I know it is very difficulty to answer that, but there is a way to estimate?