The Warm Up
Rule 7.2.1 – Prior to the match, if the teams have previously had a playing court at their disposal, they are entitled to a 6-minute warm-up period together at the net; if not, they may have 10 minutes.
(The next rule states 3 or 5-minutes if either team requests a separate warm-up).
The question is whether the warm-up before the toss qualifies as “a playing court at their disposal”? The answer is no. In international matches, “Playing court at their disposal” means “in a warm-up hall with a net in the same building as the match, for at least 40 minutes”. If they do not have this then they have a ten minute “pre-warm-up” on court (plus time before that not on the playing area)
So warm-up (through four, etc.) is 10 minutes.
How is the time shared?
Again this is not written in stone, but traditionally the 10 minutes is divided into something like 4 minutes through four, 4 minutes through two and 2 minutes serving. Some people use 5, 4, 1 minutes.
Playing should start two and a half minutes after this.