Calculating the days outside UK - Technical query request

[Puki61]

A quick question - I have 3 return flight to UK at 23:00-23:20 but had the entry stamp after midnight so next day due to awaiting in the queue at security control.

Should i count the return flight day or entry stamp day as return?

Similarly I have overnight flight from UK left 22:30 and arrived abroad country next day morning so should i count it from flight day or from the entry stamp abroad country?

Just confused if i need to prepare my list based on stamps or flight tickets. In total I am saving 3 days if i use flight dates instead stamp , and I am currently having 507 days out of 540 days and a year to apply ILR.

[zimba]

Flight date when you left the UK
UK entry stamp date when arrived back in the UK