I recently decided to suspend several Automatic Payments in YouMoney and do the transfers myself.
It was done around 7pm on the night before they were scheduled to be processed - they were scheduled for example to go out on 26/06 (after midnight) and I suspended them around 7pm on 25/06.
There were no warnings present while doing this (I checked in Classic last night, and there were no warnings in there either).
The Automatic Payments were suspended successfully (as far as I could tell) and they even disappeared off the “Next 14 days” panel in YouMoney. They are all fortnightly APs, so that makes sense.
To my shock, I discovered the next morning that the APs processed as well, which left my account somewhat overdrawn. Fortunately, these APs just move money around into different buckets in my own accounts, so I could correct the issue without too much effort.
Calling the service desk, I was told that you cannot make changes to APs after 7pm on the night before they are scheduled to be processed, and that there is a clear warning.
Like I said, I have checked again last night (both YouMoney and Classic) and could not see any warnings.