Transaction date on last bank statement

The guidance states
"The most recent bank statement must show a date within 31 days before the date of your application."

Question:
1. Please does this guidance rule apply to ILR (TIER 1 GENERAL)?
2. Will the HO look at the date of postage or the day HO received the application?
3. What happens if the public holiday prevents the application from reaching the HO on time?

many thanks