Just to help others out for those who have ATM's like the OP's. It's Article 29 Section 4...
Section 4. Up to sixty-four (64) hours of excused absence, as requested by
the employee, shall be granted for arrangements incident to a change in the
employee's official post of duty, including initial assignments, and upon
completion of initial qualifications training, regardless of whether or not
the residence is being relocated. Excused absence may be granted up to
two (2) years from the effective date of the permanent change of official
post of duty. Employees may be required to provide justification for the
use of this time. This Section is not inclusive of any time provided for
"house hunting.”
EX. #1 - I'm moving from X to Y - SHALL be approved. There's nothing your current ATM can do if you choose to take it on the front.
The 'may' portion, which is up to the ATM's discretion, deals with after you've relocated (if you didn't use all 64 hours on the initial move). COS can be used for up to 2 years following your start date. An ATM can request justification. If an ATM asks for justification, provide him/her with any number of relevant reasons (exploring this area, moving into a new house, touring schools, etc.)
As far as the debate on when you take it, it's all mental. Your hourly rate is still going to change to X on the same date regardless of if it's calculated via leave or if you choose to work it. Like others have said, I'd prefer showing up to a new facility on Day 1. Sooner is always better in my book. For those that need additional training before hitting the floor (RTF, all enroute trainees, etc), you never know when the last spot at RTF or a D-side fills up. Taking 8 days on the backend could result in someone else taking that last spot and now 8 days translates into a multi-month wait later on.