There is no Off Peak Day Return (the code for this is CDR, reflecting the fact the old name was Cheap Day Return) for this flow.
The Off Peak Return fare is set by East Midlands Trains, who want you to pay a whopping £78, which is perhaps designed to price people off the railways and make rail travel unattractive for this journey.
However you can get a combination of Anytime Day Returns (SDRs) and CDRs for much less than the extortionate through fare, saving around a third of the price, as follows:
- Warrington-Crewe SDR
- Crewe-Stafford CDR
- Stafford-Nuneatin CDR
- Nuneaton-Stamford CDR
- Stamford-Peterborough SDR
You'd need to go via those stations and the train would also need to call at each one (assuming you don't have a Season ticket).
However there is no service by this route that'll get you there by midday. You can get there by 1317 if that's any good.
You can book all of these tickets by selecting each one individually on any Train Company website, taking care to ensure that the journey itinerary matches up and you've allowed sufficient interchange time. Or you can use trainsplit.com which will take care of it all for you in one transaction, for a £2.65 fee.