There will probably be no fork to switch to bitcoin classic. The forking method used by classic is not the definitive forking method and not all hard forks will deploy this way. Soft forks also deploy differently.

Here is how it works:
After 750 of the last 1000 blocks signal support for the fork by setting a certain bit in the version number, the fork will be set to occur. After a 28 day grace period following the last block of that 1000 blocks, the fork will officially happen with the production of a block larger than 1Mb. The grace period is for everyone who hasn't upgraded to upgrade.