Ok, just been today to do my 90 day at HHI and then asked the helpful IO downstairs for up to date info. Here it is.
1. Bank letter- valid for 5 days.
2. Updated bank book including a transaction- valid for 2 days.
3. 12 months of printed statements.
So lampangguy, yes you can do it the day before as far as HHI are concerned.