Lots of threads on those questions.......
With the majority of mechanical watches the date change is a gradual process to prevent a need for a huge amount of torque (relative to what is needed to run the watch) at one moment to change the date. The date changes through an additional wheel moving into the running train to change the date and that is in the process of moving in and out of the running train between about 9pm and 2am, hence the 8pm - 3am safety zone. Using the quick set date in that period can bend or strip teeth on the wheel that engages with the running train. Some movements have an instant date change where that isn't required, but it's less common. In Breitlings the in house movement has that as mentioned above, but it is not accurate to say that only the in house has it, one or two others have an instant date change as well - Cockpit as an example.
A regular watch doesn't know how many days are in the month, it assumes that every watch has 31 days and the user has to correct for months that have fewer. Only annual calendars / semi-perpetuals have allowances in the movement for days in the month and they have issues with February. A true perpetual can handle February / leap years as well. I wrote an article on perpetuals a few years back -
http://www.breitlingsource.com/articles ... tual.shtml