There is nothing approaching quick setup and deployment at large banks.
Not Citibank, but previously worked for a financial firm that sold a copy of it's back office fund administration stack. Large, on site deployment. It would take a month or two to make a simple DNS change so they could locate the services running on their internal network. The client was a US depository trust with trillions on deposit. No, I wont name any names. But getting our software installed and deployed was as much fun as extracting a tooth with a dull wood chisel and a mallet.
This is my experience with one very large bank, but from speaking with others that have worked for/with other large banks, their experience has largely echoed mine. They tend to be very risk averse with external IT products, such as deferring critical security updates because they can't be sure what it could break and also likely don't have end to end tests for critical systems that could cost a lot of money if the upgrade fails.
I know this first hand, because you dont always know or understand whats going on in 3rd party systems. I once screwed up a 3rd party system hosted on site. I was testing an upgrade on a dev server. Part of it invovled schema changes, and I had dbo rights on both production and development servers. The hidden part that I didn't realize is that the 3rd party tool stored DB settings in your Windows roaming profile. So, because we only had 1 Windows AD domain and no otherwise network separation, even though I was on a dev box, I was talking to the prod DB. Didnt even realize it (wasn't directly evident unless you dug deep into settinga) until I started getting calls from my users, complaining of errors. This was on the 3rd of July in the US. By the time I figured out the issue, it was about 3-4am on the 4th of July.
Had to make the call of rolling forward or back. But, the supplied installer was missing some packages, so couldn't complete the install. If we rolled back, an entire days worth of tedious work by a 10 person team would have been lost. Worse yet, the tool was used by traders in Europe who were about to start their day. Being early in the morning on a US holiday, I couldnt reach their support. Couldnt even get of their EU support. I was on the phobe with my boss, his boss and the head of back office at the wee hours of the morning on a holiday.
Decision was made to hold off on doing anything until we could talk to the vendor on the 5th. Ended up rolling forward and completing the install, but I was nearly shutting myself. We were handling somewhere around 25B USD notional in bank debt for several days (which caused huge issues in PNL - proffit and loss - reporting for several business days) that we coyld take no action on.
Thought for sure I was going to be fired. But, in the post mortem, I explained everything, and it was agreed that while I shared some blame, the totality of it wasn't my fault and that because I had diagnosised it and fixed it in the most timely manner I could, I was ok. IIRC, I think the only real remediation we took to prevent a similar mishap was to disable roaming profiles on the dev server and delete all existing profiles on the dev servers...