You don't actually need to present yourself personally at the Embassy to exchange the CNI
Your Fiancee/Partner can do you provided correct ID's
Just saves a bit more time.
Also lots of stuff from NSO can be ordered online.
There's a significant amount of 'red-tape' to overcome, but as Robbie says, it's quite possible to complete within 21 days stay if you're organised.
Not much you can do about the 10 days wait for marriage licence.....just plan ahead. If your 10 days ends on a Saturday (or holiday) and the office is not open.....you can't get it till it opens.