[colmmacc]

That's a very tough call to make. Making changes at off-peak times makes some sense, especially if you think there's a likelihood of disruption. But if you're planning for the unexpected, it can be best to make changes when people are their most alert and when plenty of help is around and available. Also, in a fast moving quickly growing business, there's really only so often you can come in at very anti-social hours before burning out.