What sort of document is being printed? It's possible the printer won't necessarily begin to warm up until it gets a whole page to print. Although I realise you are saying it doesn't flash the light for up to 10 seconds.

A print job with pictures can easily run into 100-200MB. Over 100Mb Ethernet that is 10-20 seconds at raw line speed alone.

How long with something like a notepad document (which would be quite small)?

Also remember there will be some delay at Windows' end to prepare the print job and start spooling it.

It could just be that the printer takes that long to wake up - shouldn't really but maybe.

How is the printer port set up in Windows? Is it by IP or by name. It could some sort of DNS resolve issue.

Is the Mac any different to the Windows machine?