Don't look now, but...
01 Jan 2018 was a Monday; the start of a typical work week.
01 Jan 2024 was a Monday, too.
31 Dec 2018 was a Monday.
31 Dec 2024 will be a Tuesday.
All other things being equal (long weekends, holidays, etc.), there's an extra day to work in 2024 (compared to 2018) to earn one year's income.
If pays are calculated based on hours worked in each and every pay period, then you must make sure the letters claiming "annual amount" state "approximately $45000 per year".
The payroll software I was involved in developing (many years ago) allowed the pay office to specify whether the employee's pay was hourly, weekly, fortnightly, monthly or an annual amount. (And, it included quite comprehensive HR functionality, like Letters of Offer based on one set of data.)
EDIT:
Disregarding statutory holidays, there may be 20 (Feb) to 23 (Mar) working days in one month. Therefore, the basis of one's pay must be clearly stated as "$x per hour", "$x per week", "$x per month", etc. Any conversion from one time unit to another will vary considerably. Anecdotal evidence has been that competent software and/or payroll staff will, when necessary, work with "rounding adjustments" to the benefit of the payee to avoid "underpaid" complaints and the concomitant costly working hours spent resolving issues involving meager amounts.