On the Autumnwatch Messageboard, (which can be accessed via the link provided by loropo in post 16 of this thread), there are several threads referring to the change in time and format.
One such thread "Why has Autumnwatch moved to 9:00pm", was immediately directed by the BBC Autumnwatch Web Team to another thread on the AW messageboard, entitled "WHY Change The Format".
Interestingly, on that thread, (on which the concensus is overwhelmingly that both the new format and broadcast time are negative moves), The BBC Autumnwatch Web Team respond by saying "Hi all, not sure if you were aware of this but here's what Tim Scoones, the Springwatch/Autumnwatch executive producer has to say on the new format:
BBC - Autumnwatch Blog: A new shape for Autumnwatch - watch the whole of autumn with us ".
All well and good, but he makes absolutely no comment whatsoever, on the reasons for changing broadcast time, saying only: -
"The live TV shows will be transmitting weekly every Friday night at 9pm and then repeated on Saturday afternoons for families (something we're delighted to be offering this year, having listened to your comments)".
Pity then, that they don't seem to have asked for, or listened to, any comments regarding the change to 9pm.
Regards,
Mike.