Another interesting thing that always comes up is the delivery...

Another interesting thing that always comes up is the delivery of snail-mail. Not long ago, the Post Office took it upon themselves to make a conscious effort NOT to deliver mail ASAP, but to purposely delay unless a premium stamp is applied.
Really, it has always been the case, so far as I know, and I've never heard otherwise, that cheques in the mail are accepted provided the envelope is date-stamped prior to expiry, and I'd be surprised if a similar attitude wasn't taken for B.pay transactions.
A further distraction, this time, is that the expiry date is a non-business day (Saturday September 30th) usually such transactions would then be due on the next business day, but there is no mention of that issue anywhere in the LOM literature.
All in all, there are a lot of grey areas, as with anything else in life. It would be an extremely mean-spirited company secretary/BoD who took a pedantic view of the above and started rejecting funds dispatched in good faith prior to expiry, and I'll wager there would be a court challenge if they tried it on.
No, commonsense and normal good public relations in dealing with LOMOA holders dictates a minimum level of flexibility for in-good-faith transactions.
Having said that, avoid the hassles and get the money in next week.
B22.