It's there, but not it's not a straight line to the answer
Sec2: Definitions:
27. DAY
A 24:00 hour period of time, stated in local base time, specific to each base. A day is also referred to as a local base day.
Search for "local base day" and you get:
7 A. General
2. A vacation day shall be a 24 hour period corresponding to the local base day. A vacation period is a series of consecutive days posted and awarded as provided in Section 7.C. (below), and rescheduled, if applicable, as provided in Section 7.A.9. or E. (below).
and
Section 25 A. General
2. The Company shall not change the start time of any local base day to any start time other than 0130 LBT without the consent of the Association.
P.S. don't forget to make sure you calculations include the 30minute post-flight duty buffer and any applicable international buffers. Duty for a flight that blocks-in at 0105 actually ends at 0135, which is the next local base day. In your domestic case there is no bleed-over (duty ends 0115).