Meaningless question. Hotel booking business is a round the clock business if it has locations covering all continents.

This is a US-Based Hotel chain that has presence All Over the World despite its much smaller foot print that the other chains, and have its MAJORITY properties in North America.

Naturally the site should at a minimum be UP at least for North America business hours, as well as European business hours which are just a few hours time difference from the North American one.

They should also be up for Asian business hours.

In other words, they should be up 24/7 and maintenance should only be done during the least disruptive time to their worldwide customers, in particularly to their North American customers.

Or may be you think it is OK to put the site down for maintenance because it is now after business hours in Europe? That would not even work for a Banking site, let alone a hotel booking site.