My advice is to get an East Midlands Railway smartcard. It’s free of charge and arrives in a few days
Using their app you can buy a one day Travelcard and load it into the smartcard – which is literally a matter of tapping it on the back of your smartphone.
This removes the issue of worrying about being charged max fares or max time limits for your journeys and gives you the flexibility of having a one day ticket on an Oyster substitute!
Chris