Does the average punter really care how far in advance changes are notified? As long as there's a poster on the bus a week or two ahead of time, and timely social media updates, it should be fine. I can't imagine anyone planning their travel to work so far in advance unless it was a long-distance journey. From my own experience, I've sometimes only found out about timetable changes when I've actually arrived at the stop and discovered that the bus hasn't turned up as expected!
Where are you getting this "month" figure from?
According to the Government:
Run a bus service in and out of London - registering, London Service Permit, bus registration, public service vehicle operator’s licence, PSV
www.gov.uk
In a previous post you said:
Forgive me if I'm getting my figures wrong here, but 28 days' notice is required to be given to the relevant local authorities,
then at least 42 days to the Traffic Commissioner. Adding the two together gives a total of 60. That's not a month, either.