I was going to add this as a reply to the 'my DH wants to take positive DD to a football match' thread, but it's just closed due to being full.
Someone questioned if the tests on day 4 and 5 have to be 24 hours apart.
Isolation after testing positive is still ten days. You can end this isolation period early if specific criteria are met.
There's no day 4 and 5 testing. You can start testing on day 5, and once you have two negative results on consecutive days, you can end isolation early.
The earliest you can leave isolation is day 6.
Screenshot from NHS website, and also information on this page from UKGov
www.gov.uk/government/publications/covid-19-stay-at-home-guidance/stay-at-home-guidance-for-households-with-possible-coronavirus-covid-19-infection#SymptomsPositiveTest