I asked the question directly through Omega's website and received the following response the next day:
"We thank you for your message and are pleased to hear you are the owner of an OMEGA Speedmaster Professional with the reference 3573.50.
Your OMEGA is equipped with the movement 1863 and the instruction booklet describes setting the time as follows:
Pull the crown out to position 2. Turn the crown forwards or backwards. Synchronize the seconds by pushing the crown back to position 1 to coincide with a given time signal.
There is note saying the watches with various calibers, amongst 1863, do not have a "stop-second" mechanism. To synchronize, the crown should be gently turned backwards and pressure maintained to stop the seconds hand. Release when the display corresponds to the timing signal and push crown back to position 1.
This sounds a little as what you are doing when setting the time and there is therefore no problem to proceed in this way.
Wishing you a lot of pleasure with your OMEGA Speedmaster Professional, we hope to have been helpful and remain with kind regards.
Your OMEGA Team"
Just thought I'd share it with some of the newer owners of the Moonwatch.