How to calculate time taken by encryption?
The speed depends a lot  on the exact model of the processor, and on the software. New(-ish) processors with hardware support for AES are much faster than older processors without it (AES-NI in x86 processors) and an optimized implementation might be quite different from a generic one, especially if the latter doesn't even use the hardware support...



For older processors (without hardware support), some speed tests can be found here. The best numbers for Core 2 family processors were around 12 clock cycles per byte for CTR mode, which would make for about 230 MB/s at 2.8 GHz. For newer processors with AES-NI support, some numbers here, ranging from 600 MB/s to 1500 MB/s per core for CBC mode and 700 MB/s to 2600 MB/s for GCM mode with processors from 2010 to 2015 (with various clock speeds). 

(A quick and dirty test with the OpenSSL command line tool on a low-end Xeon processor from around 2012 gave figures in the same ballpark as in the previous link.)

Note that if you care about speed, it seems you shouldn't be using CBC mode. For many processors on the list (as well as the one I tested on), AES-128-GCM is quite a bit faster than AES-128-CBC. And that's without any authentication in addition to CBC encryption. I assume the reason is that CBC encryption is inherently linear: encrypting a block requires the ciphertext of the previous block. This will limit the number of parallel operations the processor can do. For the same reason, multiple cores will not help in encrypting a single, long, chain. The authentication part of GCM encryption is also fast, because there's special hardware support for that, too. (the CLMUL instructions)