calendarist
/ˌkælɛndəˈrɪst/Definitions
1. noun
A person who is enthusiastic about calendars or the study of dates and times.
“The calendarist spent hours organizing his collection of vintage calendars.”
2. noun
A person who is skilled in the use of calendars or is an expert in date and time management.
“The calendarist helped her boss manage her schedule and appointments.”