system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come online banking transactions still follow bankers hours if it's all computerized?

How come I can't pay a credit card bill that's due on a Saturday, on a Saturday?  How come it still takes 2-3 days to electronically pay bills online when I can download pretty much anything from anywhere in the world instantly?
gpt
#1 
Many systems that process banking transactions use Mainframes which process transactions in batches and more recently in Real-Time using CICS. Most banks uses software that processes banking transaction that were designed back in the late 70s-80s and still work great today.  For instance, cashing checks, although there might be an online system that displays the transaction in Real-Time, ultimately it needs to be processed and balanced in a mainframe batch by each bank at the end of their day. So, the Federal Reserve bank or ACH (Automated Clearing House) sends transactions to banks every 4 hours and then there is a delta or EOD file sent at the end of the day, say 6 PM, for banks to process all their transaction in batches; normally mainframe batches run between non-operating that start around 8PM-7AM. This is why SWIFT (same day) money transfers are expensive, they don't use the ACH system rather they use a Real-Time messaging network run by the SWIFT Organization. 

#2
Technology was designed a long time ago and modeled around how the human transaction worked and limitation around hardware. With the advent of microcomputers (your PC) and the internet, people expect transactions to happen instantaneously which requires a major overhaul of the software banks use today. That means it costs banks a lot cash in order to redesign the systems and a lot of risk given the systems work well today. For a bank it's not worth the expense and risk to make these transaction live.

#3 
By banks keeping the system rigid they can more easily garner fees from its customers as Net Interest Income drops because of the low interest rate environment and losses to other fees based on regulations on capping overdraft fees and late payments. So, a bank could lose millions by allowing its customers to pay, say a credit card bill past 5 PM the same day or allowing the cash to show up in one's account the same day rather than the next. By removing the 5pm rule, they would lose out on all the fees they charge customers that do this. The bastards.