From the Ringo web site
Charge Times: 24hrs
7 Days
All Week, 4:00am - 4:00am
£30.10
For every 1 Day Monday to Friday, 4:00am - 9:30am £6.40
1 Day Monday to Friday, 9:30am - 4:00pm £3.70
1 Day Monday to Friday, 4:00pm - Midnight £2.60
1 Day Monday to Friday, Midnight - 4:00am £2.60
For every 1 Day Saturdays, 4:00am - Midnight £2.60
1 Day Saturdays, Midnight - 4:00am £2.60
For every 1 Day Sundays, 4:00am - Midnight £1.10
1 Day Sundays, Midnight - 4:00am £1.10
1 Day Bank Holiday, 4:00am - Midnight £2.60
1 Day Bank Holiday, Midnight - 4:00am £2.60
So it looks like the fee would be £7:80 as you have to pay for three timeslots slots (Friday evening - upto midnight, Saturday night midnight to 4:00am and Saturday day 4:00am to midnight.)