Can one claim the unit costs for the entire month or only for part of this month on an "actual days basis"?

pages 394-395 in AMGA:
For partial months of recruitment, a pro-rata unit cost of 1/30 will be reimbursed for each day (for ease of implementation, each month is considered to have 30 days).
Example: If the researcher spent 20 months and 15 days on the project, the calculation for the 15 days is: 15/30 = 0.5. In this case, insert 20.5 as number of person-months.