One of my customers works for the Post Office installing the new electronic/digital sorting machines. He says that the system in the sorting office is so controlled now that there is virtually no chance of you getting a 2nd class mail delivery in 1st class time. It's against the Post Offices' interests for 2nd class to be treated in the same way as 1st class. We, their customers have to clearly see that 2nd class postage is using an inferior service time wise.
The first thing the sorting machine does is divide the mail collected from the mail boxes into first and second class bins - the second class is put to one side to be dealt with the following day. All 1st class mail coming in this day is put with the 2nd class from the previous day and delivered to the main distribution depots that evening.
These same sorting machines are also designed to sort the mornings mail for each of the posties into the quickist, shortest route which doesn't always mean doing a complete street at a time. This is the main reason why the posties are so hacked off at the moment. They have to stick to a computer generated time to complete their round, and if it takes longer, they have to finish it 'in their own time.' So each time you stop to talk to a postie, it will cost him/her as the post office don't make any allowances for chat during their deliveries.