In Foxtrot, a Slow count is thought by some to take all of two beats to produce the entire movement. According to this theory, your feet would be dividing throughout count 1, the moving foot would place on the downbeat of count 2, and the feet would be collecting (coming together) for the duration of count 2.
However, you should know that not everybody subscribes to this theory. Many people beleive this interpretation of the Slow count to be too radical, claiming that it looks off-time. They contend that the only interpretation of a slow should be of placing the moving foot exactly on the downbeat of count 1, using the duration of two beats to follow-through the step and prepare the next. According to this theory, you would need to be dividing your legs prior to count 1.
Those who do subscribe to the more "artistic" interpretation only use it in Slow Foxtrot, and to a limited degree in Tango. It doesn't apply to Quickstep or any of the Latin dances.
In Tango, it is used on any Slow count which requires development, or on any slow "snaky" or "slithery" movement. The most common applications are: Step 1 of Closed or Open Promenade, steps 1 and 4 of Open Reverse Turn lady outside, the last step of any Open Finish, and sometimes even on the basic Tango Forward Walks. It is never used in the following movements: The last step of a Closed Promenade or Closed Finish, the Slow count of a Back Rock, step 1 of Back Corte (or anything that includes Back Corte, such as Rock Turn or Prog Side Step Rev Turn).
Clear as mud?
Regards,
Jonathan Atkinson