When my WP was cancelled some 6 years ago now, I went to immigration the next day to change from Non Imm B to O on retirement. I had a warning so all my documents were correct. Nevertheless I was charged 2 days ov erstay - the day my WP was cancelled and the next day when I went to Imm. Go figure! Just a heads up.
Interesting posts above. My monthly transfers from UK government go via Citi bank and normally hit my SCB on 30th. BUT due to weekends and holidays the payment can be delayed by up to 4 days, particularly over new year eg, my 30 Dec 18 payment hit my bank 3 Jan 19. I wonder how this will be interpreted when my extension is needed December.