'Break of journey' rules are a nighmare to understand. I'd often got asked about them when I was a railway station supervisor and I usually had to check with the manager of the ticket office (which was an autonomous department). However the information from the ticket office staff often conflicted with the rules that train conductors said they had to follow. (Before anyone here blames privatisation, I'll point out the rules were inherited from British Rail!).
My own understanding of the rules is that the return portion of a single ticket must be used on a single day (but with trains running after midnight, up until 0429, still counting as part of that day's service). Further, a break of journey is usually allowed but not on some specific routes or at some specific stations. To complicate matters further, our ticket office staff always said that there was no time restriction upon the break of a journey (subject to completing the journey on the same day) but many of our ex-BR conductors maintained that such a break couldn't exceed two hours!
The National Rail website doesn't make things much clearer either. It doesn't mention having to complete a return journey within a day (but I remain reasonably confident that such a rule exists). Further, it basically says that you need to check the rules for your particular plans (about breaking your journey) to find out whether they're actually permitted or not:
http://www.nationalrail.co.uk/times_fares/ticket_types/46590.aspx
While that link tells you to phone the National Rail Enquiries Service, I doubt that most Serco staff (who handle the calls) could give you a definitive answer. I'd recommend asking at the booking office of a larger railway station (where platform staff don't also man the booking office, as they do at some smaller stations) to check the rules. If I've remembered your location correctly, Maydup, that will mean Norwich.