Why don't the people who day this is OK run it past Guinness to see what they say? Maybe they would say they would change their mind about witnesses? ;-)
A standard treadmill exercise fitness machine should be used for the attempt.
The setting of the machine is at the discretion of the competitor (but using downhill mode is not an option).
It is not permitted to lean on the "handle-bar".
The belt must be strictly stopped before the atemptee leaves the treadmill.
The venue for the record attempt must be open to the general public for the duration of the attempt
Rest breaks may be taken at the discretion of the competitor but they are included within the time for the attempt. The clock does not stop. For example, if the 24 hrs-event starts at 11 am on Monday, it must finish at 11am on Tuesday.
For the distance records (100 km, 100 miles etc.), two timekeepers should time the attempt with highly accurate stopwatches.
A log book should show the time taken for rest breaks as well as either the distances after each hour or the times after each completed kilometre or mile.
A calibration certificate for the treadmill and two signed statements by at least two sports referees should be provided.