you would be fine to leave Norwich around 2pm on that day

off-peak means in 'rush hours' like morning and evening, so on the day you go from London to Norwich as long as you travelled on the 16.00 train or earlier (so 3pm, 3.30pm would be OK) the ticket will be valid. it's called an Off-Peak Return and you can buy it when you arrive at Liverpool Street

people in the UK get very confused with this as well, it is complicated!

Posted By: s10 yellow, Sep 29, 15:12:29