The first post is actually the correct post: banks hold the money in their own pocket and use it for short-term loans to get interest on it. This way the banks earn money. In the Netherlands banks have been very open about this policy in the past. See http://nl.wikipedia.org/wiki/Valutering for the dutch wikipedia article explaining this. It also says the european payment directives from the EU put some limits on withholding money. http://ec.europa.eu/internal_market/payments/framework/psd_en.htm sets the limit to "end of next day". When you follow this rule it sets the exterme limit to 48 hours if you make your payment 1 minute after midnight and only 24 hours if you make the payment one minute before midnight.
In the Netherlands I find that when I use my debit card, the payment is made within a few hours.